Cognitive impairment occurs in 40-65% of multiple sclerosis (MS) patients, typically involving complex attention, information processing speed, (episodic) memory and executive functions. It is seen in the subclinical radiologically isolated syndrome, clinically isolated syndrome, and all phases of clinical MS. In pediatric-onset MS cognition is frequently impaired and worsens relatively rapidly. Cognitive impairment often affects personal life and vocational status. Depression, anxiety and fatigue aggravate symptoms, whereas cognitive reserve partially protects. Cognitive dysfunction correlates to brain magnetic resonance imaging (MRI) lesion volumes and (regional) atrophy, and degree of and increase in MRI abnormalities predict further worsening. Experimental MRI indicates a crucial role for (focal) cortical lesions and atrophy, abnormal cortical integrity, and early changes in normal appearing brain tissue. Functional MRI suggests compensatory reorganization and adaptation changes in neural activities. Screening tools are the Brief Repeatable Neuropsychological Battery, Symbol Digit Modalities Test and Audio Recorded Cognitive Screen. The Minimal Assessment of Cognitive Function in Multiple Sclerosis (MS) is used for formal neuropsychological evaluation. What constitutes a clinically relevant change and how to optimally monitor cognition are issues to be settled. In relapsing-remitting MS timely and adequate disease modifying drug treatment may stabilize or possibly improve cognition. There is no evidence-based symptomatic drug treatment, nor are there optimal non-pharmacological approaches. Leisure activities enhance cognitive reserve. Cognitive rehabilitation in MS patients is still in its infancy. Cognitive behavioral therapy, exercise, and education programs are promising psychosocial interventions to improve coping and lessen cognitive symptoms.