This chapter updates our knowledge of the short- and long-term effects of cannabis on cognition based on integrating evidence from the most recent literature on this topic. Numerous studies have examined the acute effects of cannabis on human cognition. Cannabis induces perceptual distortions and impairs memory and concentration during acute intoxication. Studies of long-term and heavy cannabis users have continued to investigate residual or persistent effects of cannabis on cognitive function. Verbal memory is consistently impaired in chronic cannabis users, with impaired performance on word list learning tasks. It might be expected that people with schizophrenia who are already cognitively impaired may be even more vulnerable to the adverse effects of cannabis on cognition. Cognitive functions, encompassing attentional, memory, executive and inhibitory processes are impaired during both acute intoxication period and following long-term use of cannabis.