This paper revisits and revitalizes Nerlove's (1965) efficiency measure, which is based on profit maximization and decomposed into price or allocative efficiency and technical efficiency. The authors introduce the directional technology distance function, a generalization of Luenberger's (1992b, 1995) shortage function and Blackorby and Donaldson's (1980) translation function, to provide a more modern framework that allows for multiple inputs and outputs. The directional technology distance function is shown to be a complete representation of a technology with free disposal of inputs and outputs. The paper discusses the dual relationship between the directional technology distance function and the profit function, providing a streamlined proof of their dual correspondence. It also demonstrates how the directional technology distance function can be used to represent Nerlove's efficiency measure, leading to a decomposition of profit efficiency into allocative and technical efficiency. The paper concludes by discussing the properties and applications of the directional technology distance function in efficiency measurement.This paper revisits and revitalizes Nerlove's (1965) efficiency measure, which is based on profit maximization and decomposed into price or allocative efficiency and technical efficiency. The authors introduce the directional technology distance function, a generalization of Luenberger's (1992b, 1995) shortage function and Blackorby and Donaldson's (1980) translation function, to provide a more modern framework that allows for multiple inputs and outputs. The directional technology distance function is shown to be a complete representation of a technology with free disposal of inputs and outputs. The paper discusses the dual relationship between the directional technology distance function and the profit function, providing a streamlined proof of their dual correspondence. It also demonstrates how the directional technology distance function can be used to represent Nerlove's efficiency measure, leading to a decomposition of profit efficiency into allocative and technical efficiency. The paper concludes by discussing the properties and applications of the directional technology distance function in efficiency measurement.