This review highlights the research carried out during the last decade or so in the field of anion coordination using cyclen-based lanthanide complexes as luminescent receptors (cyclen = 1,4,7,10-tetraazacyclododecane). Herein, the fundamental concepts explaining the particularly good affinity between cyclen derivatives and lanthanides and the way to sense the interaction with anionic substrates are firstly discussed. This is followed by a selection of examples from the recent literature describing these cationic receptors as powerful optical sensors of environmental, biological and pharmaceutical relevance.