It is an old idea in ecology that environmental change can induce rapid transformations at times impossible to reverse. Early manipulation experiments hinted that coastal communities could organize into different distinct configurations after a disturbance (Dayton 1971). Along these lines, a theory of multiple stable states had been developed (Holling 1973; Lewontin 1969) to explain patterns in coral reefs, semiarid ecosystems, shallow lakes, or fisheries (Scheffer et al. 2001), even if experimental evidence for alternative states has been debated (Schroder et al. 2005). Nonetheless, the intuition behind the possibility of shifting between alternative attractors at the cost of small interventions (aka small events can have big consequences) has precipitated from ecology, to the study of climatic events, social transformations, and even to the way of understanding banking systems. These ideas have led to lively discussions about the possible existence of tipping points at which ecological systems may “fall off” to a different regime that may be difficult to escape. Current high rates of extinction events, rapid environmental changes, high desertification risks, a potential for climatic shifts, and even financial collapses have also made critical transitions of high interest. Suggestions have been made that even the entire biosphere may be approaching a critical transition (Barnosky et al. 2012). Therefore, being able to quantify the resilience of ecological systems (i.e., the amount of disturbance ecosystems can undertake before shifting to alternative state) can be a promising management strategy for avoiding abrupt unexpected transitions. However, our ability to quantify ecological resilience is still questionable. In the last 5 years, theory has suggested that we may be able to derive early warning signals derived from time series in systems that are about to experience a critical transition (Scheffer et al. 2009, www.early-warning-signals.org). Most of these ideas are reinterpretations of well-understood dynamical properties that unfold close to bifurcation points. But the fresh innovative features have created momentum for developing new methods and for studying a broader range of tipping points both in theory and practice. In this issue of Theoretical Ecology, we focus on this emerging field of critical transitions with an emphasis on measuring the resilience of ecological systems and the possibility of anticipating critical transitions. Boettiger et al. (2013) classify the so far work on early warnings and identify uncharted grounds in the study of critical transitions. Part of the uncharted grounds is covered by exploring how time delays between drivers and environmental variables affect the behavior of early warnings (D’Odorico et al. 2013; Guttal et al. 2013), how transitions from cyclic to noncyclic regimes and vice versa can be anticipated (Batt et al. 2013), and how traveling waves may start propagate and can be detected to signal the expansion of invasion fronts (Kuehn 2013). These studies shed light on aspects widely encountered in real ecosystems that hinder or completely cancel our ability to identify any approaching transitions. Another potential signal is flickering, the occasional excursion of an ecosystem between alternative states, which is probably most frequently encountered under natural perturbation regimes. Dakos et al. (2013) show that, under flickering, early warnings are to be interpreted with caution, while other indicators may serve as better signals. But still, the work on critical transitions and their precursors is at its infancy. Is there a potential for using these approaches in more complex cases? Hefley et al. (2013) further develop state approaches to detect early warning signs for shifts and demonstrate their utility in a specific system of V. Dakos Integrative Ecology Group, Estacion Biologica de Donana, c/ Americo Vespucio s/n, 41092 Sevilla, Spain e-mail: vasilis.dakos@ebd.csic.es