This paper introduces Pick-A-Mood, a character-based pictorial scale for reporting and expressing moods. Pick-A-Mood consists of three characters that each express eight mood states, representing four main categories: excited and cheerful (for energised-pleasant), irritated and tense (for energised-unpleasant), relaxed and calm (for calm-pleasant), and bored and sad (for calm-unpleasant). Using Pick-A-Mood requires little effort on the part of respondents, making it suitable for design research applications in which people often have little time or motivation to report their moods. Contrary to what is often assumed, mood and emotion are distinct phenomena with different measurable manifestations. These differences are discussed, and a review of existing methods is provided, indicating to what extent current methods that measure emotion are suitable for measuring mood. The development and validation of Pick-A-Mood is reported, and application examples and research opportunities are discussed.