The collection of papers in the 2015 edition of Addiction Reviews explores molecular, imaging, genetic, therapeutic, and epidemiological aspects of addiction. For example, a review by Gonzales and Smith discusses some of the key morphological, synaptic, and functional differences between cholinergic interneurons of different striatal regions and across species, and considers the potential impact of striatal cholinergic dysfunction in cocaine addiction/abuse. In another review, Subramaniyan and Dani focus on the acquisition phase of smoking addiction and review animal studies on how nicotine modifies dopaminergic and cholinergic signaling in key nodes of the reinforcement neurocircuitry. Fedota and Stein discuss evidence of coherent modulations in resting-state functional connectivity at various stages of nicotine addiction, suggesting potential network interactions on which to focus future addiction biomarker development. And a review by Uhl and colleagues discusses data from genetic and genomic studies of addiction to highlight the ways in which variation in human cell adhesion molecules may contribute to addiction. The reinforcing actions of aggression and alcohol are discussed in a review by Miczek et al., who also link alcohol and aggression to a deficiency in brain serotonin and provide insights on the modulatory action of neuropeptides and neuroactive steroids on alcohol and aggression. Lastly, in a review by Lopez-Quintero and Anthony (epidemiologists who study foodborne illness outbreaks), the foodborne outbreak approach is adapted to develop new estimates of drug use disorder risk for single-drug and polydrug users.