In the recent years many disasters and catastrophic events such as hurricane Mitch, tsunamis, SARS, terrorist attacks and earthquakes have shown that we live in world with increasing uncertainty. These events can cause major disruptions in the supply chain. Although similar events have occurred, since the terrorist attacks of September 11 of 2001 the firms began to reassess the benefits of commonly accepted strategies for sourcing, transportation, demand, planning and managements in a stable environment (Martha and Subbakrisha 2003).In a competitive environment many firms have developed global supply chains which are complex to manage and vulnerable to disruptions. The literature has documented many cases of what can possible go wrong in this supply chains due to unexpected events and what can we learn. For example, Ericsson lost 400 millions euros and the dominant position in the mobile phone market because the managers misestimated the consequences of a fire suffer by their semiconductor supplier’s plant in Albuquerque (Chopra & Sodhi (2004, Rice and Caniato (2003).Norman and Jansson (2004) follow up this case and show how Ericsson implemented proactive supply risk management. Supply chain disruptions can potential compromise facilities, equipment and human resources and the value of stock market shares. Consequently, some studies have quantified the repercussions both in the short and the long run of disruptions in the supply chain. For example, Rice and Caniato (2003) present the results from a company survey that estimates a $50 million to $100 million cost impact for each day its supply network was disrupted.Hendricks and Singhal (2005) analyze the stock market reaction when firms publicly announce they are experiencing disruption during 1989–2000. On a sample of 827 the authors find that one year before through two years after the disruption announcement date, the mean abnormal return of their sample firms was from 33 – 40%. The author point out that their results suggest that the firms need to invest and develop capabilities and infrastructure that allow them improve reliability and responsiveness in their supply chainThe associated operation and financial risk of supply chain disruptions has been an increasing interesting topic for doing research for academic and practitioners (Craighead et al (2007). The dynamic and evolving nature of supply chain risk does not allow being free of vulnerability (Peck 2005) so it is important to design supply chain that can overcome disruptions and adapt a changing environment. This supply chain is called “resilient” and there is an increasingly number of papers that discuss the main strategies to build resilient supply chain.The main propose of this paper is to survey the literature in resilient supply chain and try to identify possible research opportunities. Managers Perceptions Catastrophic events and disruption had occurred form a long time and managers are aware of their economic and operational consequences. For example, Knight and Pretty (1996) found that the impact of a disruption on shareholder was a sharp decrease of almost 8% and a recovery time (if recovery is possible) of 50 trading days.Despite manager’s recognition of the importance of risk assessment, little investment of resources and time for mitigating supply chain risks have been done. Research has found that is difficult to perform cost/benefit analysis or return on investment analysis to justify certain risk reduction programs or contingency plans (Closs and McGarrell (2004), Rice and Caniato (2003)). Consequently, passive acceptance is often the default strategy even when it is not appropriate (Tomlin 2006).Furthermore as Repenning and Sterman (2001) point out firms rarely invest in improvement programs in a proactive manner because ‘‘nobody gets credit for fixing problems that never happened. ’’ In a recent survey (Poirier and Quinn 2004) found that only 33% of firms responded that they paid “sufficient attention to supply chain vulnerability and risk mitigation actions. Moreover, Mitroff and Alpaslan (2003) present research on preparing for terrorism and state that only between 5% and 25% percent of Fortune 500 companies are prepared to handle crises or disruptions.The answer of how to improve security without jeopardizing supply chain effectiveness can be found in the quality movement (Lee and Wolfe ( 2003)) . Disruptions Drivers, Vulnerabilities and Security Initiatives In this section we briefly show the frameworks, security initiatives and analytical models for assessing risk and mitigating disruptions that have been developed in the literature. • Iniciatives Many authors (Tang (2006a), Lee and Wolfe (2003) and Rice and Caniato(2003)) have explained security initiatives to improve the supply chain security developed and launched by US government after the terrorist attacks.Two important initiatives are: Container Security Initiative launched by US Customs in 2002, allow firms to target conducted at foreign ports before loading and examine high risk-overseas before arrive US ports and Customs –Trade Partnership Against Terrorism (C-TPAT) certificated programmed was established by Customs in 2002. Certificated firms will have the benefit of reduce cargo exams. These initiatives have raised some concerns. For example, Rice and Caniato (2003) pint out that security requires a continuous commitment and effort of many parties. • FrameworkDatta and Allen (2005) develop a multi-dimensional framework of supply chain resilience based on concepts from diverse fields of research. The framework captures two main aspects of a resilient supply chain: the capacity to maintain the production system when a disruption the agility to respond to changes in the environment and customer requirements. Then the authors model the supply chain as a complex system and used multiple adaptive agents that were able to coordinate and adapted to different business scenarios. Chopra and Sodhi (2004) show 8 categories of supply chain risk and their drivers.Disruptions, one of the categories, have these drivers: Labor dispute, supplier bankruptcy, war and terrorism, dependency on a single source of supply as well as the capacity and responsiveness of alternative suppliers. The author used scenarios methodology (what if) to understand the impacts in each risk categories and then show suitable effective mitigation strategies. Peck (2005) using in-depth exploratory case studies and depth interviews find that there is a little understanding of the scope and dynamics of the vulnerability.She proposed an integrated framework that has four levels of analysis: value stream/product or process; asset and infrastructure dependencies; organizations and inter-organizational networks; and social and natural environment. She states that, the resilience of the network should be asses focusing on critical operational assets at stage two. Sheffi and Rice (2005) determines the profile of a disruption where the show the different stages of a disruption form preparation to long term-impact.They also develop a vulnerability assessment where a firm can map the different disruptions into four quadrants that are form by the interaction of the potential consequences and the disruption probability. Kleindorfer and Saad (2005) the author develops a conceptual framework (SAM) for managing supply chain risk which considers the three tasks: Specifying sources of risk management, Assessment and Mitigation. The authors introduce 10 principles to implement SAM. Based on empirical results from U.S Chemical industry, the author point out that reducing the frequency and severity of risks faced and increase the capacity supply chain participant is important dimension in disruption risk management in supply chains. Craighead et al (2007) develop six prepositions that show that the severity of the impact of a disruption is moderated by three supply chain design characteristics density, complexity, and node criticality and two supply chain mitigation capabilities of recovery and warning. • ModelsTomlin (2006) shows different financial tactics and operation mitigation and contingency tactics that a firm can use to manage disruptions. Mitigation tactics refers to an action that firm performs before the disruption occurs and contingency tactics when the disaster occurs. He develops a supply chain model that considers a single product firm which can source from two suppliers, one reliable and another unreliable. He finds that the percentage uptime and the frequency and length of the disruptions are key determinants of the optimal policy.Wu et al (2007) present a model called Disruption Analysis Network (DA_NET) that used a Petri net approach to model a supply chain system and its disruptions. The authors state the use of DA_NET can be used to understand the propagation of disruptions and how do they affect the operational performance of the supply chain such as: cost or leadtime. Defining Resilience in Supply Chains Resilient is a well known concept in disciplines such as: ecology, psychology and mechanical engineering. Coutu (2002) introduces the concept of organizational resilience, which can be defined as “the ability to bend and bounce back from hardship”.Some definitions of resilience related with supply chain are: Christopher and Peck (2003) define resilience as “the ability of a system to return to its original state or move to a new, more desirable state after being disturbed’. Implicit in this definition is the notion of flexibility, and given that the desired state may be different from the original, ‘adaptability’ One of the most powerful ways of achieving resilience is to create networks, which are capable of more rapid response to changed conditions. This is the idea of agility.Christopher (2004). Mitroff and Alpasan (2003) state that resilient organizations are ‘crisis prepared (or proactive)’ encounter fewer disasters and recover better from hardship. Sheffi defines resilience as “the ability of a company to bounce back from disruptions”. From the definitions we can notice that resilience have two main characteristics: The capacity to overcome a disruption minimizing the impact and respond to changes in the environment to gain control of the opportunities (Datta and Allen (2005)). Building ResilienceMost of the research recreates short cases were the introduce strategies implemented and developed by many firms. For example, postporment strategy (Lee (1996)) has appeared in many papers (Lee and Wolfe (2003), Tang (2006a)) and illustrated the cases of Benetton and HP deskjet printers. The first papers do not explicitly introduce the term resilience but recommend strategies that are used to secure the supply chain, some of these strategies were also are incorporated in latter papers of resilient supply chain.Following we will briefly summarize the papers that have shown strategies to build resilience in supply chains. Yossi Sheffi (2001) determines the challenges that the firms face in this new environment. The author establishes that redundancies is one possible operate alternative to deal with the terrorist attacks. The paper identifies and discusses some important trade-offs: • Redundancy vs. efficiency. • Centralization vs. dispersion. • The lowest bidder vs. the known supplier. • Government cooperation vs. irect shareholder value. • Managing risk vs. delivering value. Juntter et al. (2003) find that for mangers handling tradeoff is very relevant. Therefore, they claim further research in the ones propose by Sheffi (2001) and develop decision making tools in supply chain. Martha, J. and Subbakrishna, S. (2002) discuss the following strategies to mitigate risk: cultivate sourcing alternative, insure the risk if you can ,line up alternative transportation, manage inventory right level ,build in quick respond to shifts in demand.Lee and Wolfe (2003) discuss fix mitigating strategies for the effects of a security breach when it occurs. These strategies are: • Comprehensive Tracking and Monitoring • Total Supply Network Visibility. • Flexible Sourcing Strategies: Create a local supply source, develop multiple source component sources for the same component or input material and use supplier with more the one manufacture site to supply materials. • Balance inventory management. • Product and Process Redesign: Standardization and Postponement • Demand Based ManagementChristopher and Peck (2004) describe 4 four principles to create resilience supply chain and in each they determine some key elements: • Supply chain (re) engineering: Supply chain understanding, supply chain design principles and supply base strategy • Supply chain Collaboration: Collaboration planning and supply chain intelligence • Agility: visibility and velocity and acceleration. • Create a supply chain management culture: continue teams, board- level responsibility andf leadership and factor risk consideration into decision makingRice, J. B. and Caniato (2003) states that resilience can be build be flexibility and redundancy. Redundancy is achieved by maintaining capacity such as: inventory, additional production lines, qualifying and maintaining multiple suppliers, maintaining a dedicated transportation fleet in order to respond to a disruption. The authors state that flexibility is achieved by creating capabilities in the firm’s organization to respond by using existing capacity that can be redirected or reallocated .They also show advantages and disadvantages of different strategies to build resilience for each of the possible disruptions (supply, transportation, production facilities, communication and human resources) that a firm can face in the supply chain. Sheffi (2005) points out that resilience can be achieved by increasing redundancy, building flexibility and changing corporate strategy. He shows actions in each of these strategies. • Redundancy: • Flexibility: Postponement, Standardized process, Concurrency process. Culture Change: Continuous communication, empowerment, passion for work, conditioning for disruptions Peck (2005) states that for a firm to remain truly resilient need slack in the system in the form of inventory, capacity, and capability and even time, plus constant awareness and vigilance. This confirms the importance of redundancy. Lee (2004) study more than 60 successful supply chains around the world and found out that they shared main three characteristics: agility, adaptability and aligned. He introduced a new concept “The Triple-A Supply Chain”.We can observe that authors have explicitly discussed the first two characteristics as principles to build a resilient supply chains. Some elements of alignment have been explicitly mention resilient supply chain literature. Robust strategies for mitigating disruptions Tang (2006b) introduces the concept of robust strategies have two main proprieties: efficiency and resilience. This means that robust strategists are a subset of the resilient strategies and do not consider redundancies. Tang (2006a) discuss eight robust strategies that have been used by ifferent firms : Postponement, strategic stock, flexible supply base, make and buy, economic supply incentives, flexible transportation, revenue management, dynamic assortment planning and silent product rollover. Table 1 summary of Strategies for building resilient supply Chains |Papers |Methodology |Resilience Strategies | |Christopher and Peck (2003) |Case studies and interviews |Four principles | |Rice, J.B. and Caniato (2003) |Case studies and interviews |Flexibility and redundancy | | | |Strategies depending in the disruption | |Sheffi (2001, 2005) |Case studies and interviews |Redundancy flexibility and culture change. | | | |It is important to consider Trade offs | |Martha, J. nd Subbakrishna, S. |Case studies |Idea of Just in Case, strategies that creates redundancy. | |(2002 | | | |Lee and Wolfe (2003) |Case studies |Introduce how to implement security in supply chain following the path| | | |of the quality movement. | | |fix mitigating strategies for the effects of a security breach | |Tang (2006 a) and (2006b) |Survey papers |Robust strategies =resilient and cost effective. | | | |Eight robust strategies | Conclusions Two big project that provided important knowledge in resilient supply chain are: the first was developed during three years by Sheffi, Rice, Cianiato nd other researchers at MIT center of transportation of MIT and the second sponsored by UK government and developed by Christopher, Peck and other researchers at Cranfiled University. The primarily methodology for studying resilient supply chain is based on cases and interviews and many studies have discussed the same strategies. As Blackhurst et al (2005) states the literature related to supply-chain disruptions is informative. Consequently, they are some research opportunities in this topic that has an increasingly interest for academia and practitioners.For example INFORMS 2006 annual meeting one of the sessions was dedicated to this topic “the resilient enterprise- Challenges in supply change security and resilience” Future research There are many opportunities for future research. Some interest topics can be: • How to evaluate the disruptions (low-probability/high-impact) • How can we create resilience we the introduction of new technologies for example, (RFID) • Empirically determine why some companies adopt resilient practice and other do not (Importance supply chain in the firm) • Develop measures or metrics for resilient (do resilient enterprise performs better).It would be difficult to actually have a metric for resilience or vulnerability in the supply chain that can capture all the potential risks that a firm faces under such disruptions. • Alliances among suppliers and supply chains. • Humanitarian logistics , what can resilient enterprise learn. • Which elements in common have the companies that are consider resilient. (which strategy is more applied) • How to create resilience in services operations.