Restless legs syndrome and periodic limb movement disorder are common neurological entities that may be associated with insomnia and excessive daytime sleepiness. This chapter reviews the clinical features, natural history, laboratory investigations, genetics, pathology, and management of primary restless legs syndrome (RLS) and periodic limb movement disorder (PLMD). Large epidemiological surveys have shown that self-reported symptoms of RLS were correlated with sleepiness. Electrodiagnostic testing with nerve conduction studies and electromyography are useful to detect subtle peripheral neuropathies. Several factors suggest that impaired dopaminergic function and iron homeostasis underlie the pathophysiology of RLS. One study demonstrated that dopaminergic treatment of RLS patients improved both RLS severity and sleepiness as measured by multiple sleep latency test (MSLT) score. Considerable research has been directed towards elucidating the basic mechanisms and optimizing the management of RLS and PLMD.