The article registers considerable attention to the categories of «effectiveness» and «efficiency», which are widely used for the assessment and management of manufacturing and service activities. However, it is noted that among modern scientific works, there is considerable confusion in the interpretation of these concepts, which impedes their adequate usage. In this regard, the author sets himself three tasks: to clearly identify both categories, define their mutual relations and explore the possibilities of their combined use for the above designated purpose. The solution of these tasks will provide the basis for better use of these categories collectively. The article provides an overview and analysis of dictionary definitions of such concepts as “result”, “effect”, “effectiveness” and “efficiency”. It also provides a survey and analysis of the most similar English equivalents. The article discusses a number of scholarly works specifically devoted to the study of these concepts. A comparative table of the views of a wide range of different authors regarding the definition of these concepts is compiled. As a result of performing the comparative analysis of these opinions a number of quite specific definitions of the given concepts is revealed, allowing one to solve the first problem. To solve the second and third tasks, we propose a new conceptual representation of activity in which both categories are linked via the key category of «mission». The authors propose updated definitions of the concepts in question and identify their priorities. The fundamental content of the activity category «mission» is clarified. The authors balanced the semantic structure for the formulation of «mission». A set of various measurements are proposed for for the study of the concepts.