In this article I develop a phenomenological model of the dynamics of mind-wandering based on Aron Gurwitsch's (1964) field theory of consciousness. Specifically, I articulate these dynamics in terms of conscious field transformations resulting from particular interactions between the attentional focus, contextual background, and non-contextual background -- structures that Gurwitsch understood as invariantly present. According to the model, during guided thought the conscious context that escorts the focus of attention behaves like an autonomous self-defining system, as the primary determinant of (...) its own subsequent states. Often, during episodes of mind-wandering this autonomy is lost as the theme interacts preferentially with the margin. Additionally, I explain the relevance of mind-wandering to Varela's (1999) neurophenomenology of time consciousness. When the stream of consciousness is guided and constrained, as in cases of deliberate or ruminative thinking, retentions are derived primarily from information contained in the thematic field. When the stream of consciousness wanders, moment-to-moment retentions often derive mainly from marginal cognitive information stored in the outskirts of the field of consciousness. (shrink)