This thesis investigated the neural correlates of the influence of mood states on sensory processing and decision making. How mood states affect the processing of simple sensory stimuli and their underlying neural correlates is still unclear. To address this question, sensory stimuli were presented to healthy participants after the induction of a happy or sad mood, while their brain activity was recorded using fMRI. The results demonstrated that happiness and sadness have differential effects on the processing of simple sensory stimuli. The second experiment investigated the impact of mood states on monetary decision making. Eighteen participants performed a gambling task in an fMRI scanner after the induction of a happy or a sad mood state. The results showed that a happy mood state promotes gambling, and that happy and sad mood states exert opposite effects on reward and emotional brain regions, with the latter being recruited for more difficult decisions.