This paper describes a hypothesis of Tronick's (2002) that positive and negative affect activation waves with changing amplitudes based on positive and negative lived experiences are the sources of persistent or regularly recurrent moods of feeling upbeat or downbeat. The characteristics of discrete affects, moods, and affect states are discussed in the light of a previous study based on clinical observation (Lichtenberg, Lachmann, and Fosshage 1996). The clinical experience theory underpinning that study is then compared with Tronick's Sanderian activation wave theory. A case example is presented, and the overall relevance of Tronick's theory to clinical work is discussed.