The laws of equilibrium statistical mechanics impose severe constraints on the properties of conventional materials assembled from inanimate building blocks. Consequently, such materials cannot exhibit spontaneous motion or perform macroscopic work. Inspired by biological phenomena such Drosophila cytoplasmic streaming, our goal is to develop a new category of soft active materials assembled from the bottom-up using animate, energy-consuming building blocks such as kinesin molecular motors and microtubule filaments. Released from the constraints of the equilibrium, these internally driven gels, liquid crystals and emulsions are able to change-shape, crawl, flow, swim, and exert forces on their boundaries to produce macroscopic work. In particular we describe properties of an active fluid that upon confinement transitions from a quiescent to a spontaneously flowing state. We characterize the properties of the emergent flows as well as how the transition to a flowing state depends on the properties of the confining geometry. Our results illustrate how active matter can serve as a platform for testing theoretical models of non-equilibrium statistical mechanics, developing new microfluidic applications and potentially even shedding light on self-organization processes occurring in living cells.