 What follows is organized into five sections. In §1, we trace key points of the historical trajectory whereby determination came to be seen as a distinctive form of specification. In §2, we present the commonly advanced features of determinables, determinates, and their relation; here also we discuss extensions of the (realistically construed) relation to ontological categories beyond properties. In §3, we sketch the main anti-realist, reductionist, and non-reductionist accounts of determinables and determinates, saying how these aim to accommodate the seeming features of determinables and determinates, and flagging key concerns and responses; here also we discuss certain accounts of the structure or logic of determination. In §4 we consider reasons for and against thinking that determinates are metaphysically prior to determinables. In §5 we present three applications of these notions, on which the distinctive features of determinables and/or determinates are seen as key to understanding physical laws of nature, mental/higher-level causation, and metaphysical indeterminacy.