This essay reviews the use of the competency concept in various educational and professional development contexts. Its key purpose is to identify the lessons that computing education and practice can learn from disciplines that have explored and evaluated the use of competency-based approaches much longer than computing. The review reveals a broad variety of definitions and uses of the competency concept in a number of fields but no single unifying success formula emerges. The key recommendations of the essay are as follows: the efforts in computing education that use a competency-based approach should 1) carefully consider ways to specify competencies in an integrated, holistic way instead as a simple combination of components (such as knowledge, skills, and attitude); 2) recognize the purpose and timeframe for which competencies are specified, specifically avoiding a sole focus on short-term professional competencies; and 3) explicitly and transparently communicate whether or not the intent of any effort that uses a competency-based approach is to transform the entire educational model (instead of simply using competencies for specifying outcome expectations).