A prominent but under-appreciated concern for individuals with schizophrenia and psychotic disorders using cannabis is the co-use of tobacco. Rates of cannabis and tobacco co-use are on the rise, which may reflect the changing legal landscape surrounding cannabis use. Currently, there are no approved medications for cannabis use disorders and behavioural treatments yield only modest abstinence rates that decline once treatment is discontinued. Converging evidence suggests that treatments for cannabis use disorder may be augmented among co-users if tobacco use is considered and addressed, highlighting the need for a better understanding of cannabis use in the context of tobacco. This chapter reviews the evidence for: (1) mechanisms facilitating the high rates of tobacco use among cannabis users, including those with psychosis; (2) the interactive effects of co-use on the brain, clinical outcomes, and physical health; and (3) the implications for treating cannabis and tobacco co-use in general, and in psychotic disorders in particular. Overall, we present evidence that attests to the public health significance of cannabis and tobacco co-use and the urgent need for the development of empirically informed treatments for these individuals, particularly for those with co-occurring psychosis.