Computerized cognitive training (CCT) to improve cognitive functioning is of enormous interest and has been applied in a broad range of populations with goals of improving both cognition and community functioning. Recent reviews presenting negative conclusions about CCT efficacy have inconsistent definitions of the treatment targets and cognitive improvement. They do not present an accurate representation of the typical process of CCT and cognitive remediation (CR), especially as delivered in major mental illnesses such as schizophrenia. This review provides guidance on the definitions of CCT and CR, the uses of CCT and CR, and the definitions and measurements of cognitive and functional gains. The review focuses on schizophrenia and healthy aging, with each population receiving unique CCT or CR approaches and substantial extant literature with which to elucidate fundamental CCT and CR concepts and research findings. It is our conclusion that CCT has been shown in most studies to improve cognitive performance on untrained tests in healthy older people and in people with schizophrenia. Functional gains in schizophrenia appear to be limited to CR studies. Clearly defining CCT, CR, and levels of treatment-related gains will be critical for understanding the benefits of these widely used treatment programs.