This chapter describes recent developments in the analysis of kappa opioid receptor (KOR) function at a molecular, cellular and systems level within the central and peripheral nervous system. A combination of neuroanatomical, electrophysiological and behavioral techniques have been used to probe the functional consequences of KOR activation in the brain and spinal cord in both normal and pathological conditions. As a result of a number of studies conducted over the last three decades it is apparent that kappa opioid receptors will emerge as an important therapeutic target for both psychiatric and neurological pathologies. The following chapter reviews where the field has been, but importantly discusses gaps in our knowledge and highlights important new directions for the future.