Ketamine is an arylcyclohexylamine derivative recognized for its analgesic, rapid antidepressant, psychoactive, sedative, and hypnotic properties. Ketamine is composed of two optical isomers, (R)- and (S)-ketamine, which function primarily as N-methyl-D-aspartate (NMDA) receptor antagonists. Ketamine interacts with numerous other receptor targets and exerts effects on complex neurobiological processes. In the last decades, ketamine has solidified its role in human and veterinary medicine as a versatile anesthetic. Since the first clinical trial demonstrated the rapid antidepressant effects of ketamine in 2000, the study and clinical use of ketamine have gained traction in new therapeutic areas. Significant advances have also been made in understanding ketamine’s actions; however, the precise mechanisms underlying its effects remain elusive. This chapter focuses on findings relevant for understanding the dose-dependent pharmacological and neurobiological effects of ketamine in order to offer insights into its anesthetic and psychoactive effects, as well as its antidepressant action. These mechanisms include modulation of excitatory and inhibitory neurotransmission, impact on monoaminergic and other neurotransmitter systems, and influence on cellular signaling pathways. The chapter also addresses limitations of translational preclinical research, highlighting challenges and considerations necessary for advancing the understanding of ketamine’s effects.