Schizophrenia is considered a severe mental illness characterized by the presence of positive, negative, and cognitive symptoms. Thus, it affects various cognitive domains, including basic cognition (attention, processing speed, memory, working memory, reasoning, problem-solving), social cognition (understanding social cues, emotions, and intentions of others), and metacognition (self-awareness, insight into abilities, and the capacity to monitor and adjust cognitive processes). The course of cognitive decline in schizophrenia remains under investigation. Different trajectories, including stable impairment, progressive decline, improvement, and fluctuating courses, have been proposed. Early intervention programs are crucial to optimize recovery and limit disability, as cognitive deficits are present during the prodromal and early stages of the illness. In chronic stages, while some studies suggest possible improvement in specific cognitive domains, others indicate stability or even decline, particularly with persistent and pharmacologically resistant symptoms. Cognitive impairment is considered a core symptom as it is present from the illness onset and it significantly impacts daily life, hindering academic and occupational performance, social functioning, and treatment adherence. Cognitive reserve is a potential factor that may explain clinical, cognitive, and functional differences among patients. Evidence suggests that patients in both early and late stages with higher cognitive reserve show a later onset of the illness and better outcomes in cognition and functionality. Finally, psychical exercise and cognitive remediation programs are gaining traction as they address these core deficits and improve patients’ ability to live independently and participate in society.