Anorexia nervosa (AN) is a mental illness characterized by continuously severe, self-imposed starvation and intense anxiety, manifested as fear of gaining weight. An increasing number of individuals are diagnosed with AN, especially among men. AN is now recognized to include those serving the military as well. With no accepted pharmacological treatments available, coupled with its high mortality and relapse rates, better understanding of the neurobiological basis of this mental illness is needed. This chapter describes the animal model of AN, called activity-based anorexia (ABA), that captures multiple core features of AN successfully, including voluntary food restriction, heightened anxiety, and excessive exercise, culminating in severe body weight loss. Also described in this chapter is how individual differences in vulnerability to ABA can be quantified. This chapter will include examples of synaptic plasticity measurements that may underlie the gain of resilience, quantified as the suppression of two maladaptive behaviors – excessive exercise and voluntary food restriction. Finally, the chapter will describe potential uses of the ABA model for exploring pharmacological treatments to reduce the maladaptive behaviors elicited in the ABA model.