This paper invokes a poststructuralist lens--and, in particular, Foucauldian ideas--in conceptualizing teacher emotions as "discursive practices." It is also argued that within this theoretical framework, teacher identity is theorized as constantly becoming in a context embedded in power relations, ideology, and culture. In terms of the methodology used when studying teacher identity and emotion through this lens, it is shown that long-term ethnographic investigations offer important advantages. This is shown through an ethnographic study of the emotions of teaching with one teacher over three years (1997-1999) and a semester long follow-up study with the same teacher four years later (spring 2003). The contribution of this study in what is presently known about teacher emotions in educational settings consists in the following three ideas: first, that emotional rules in teaching are historically contingent; second, that a teacher plays a part in her own emotional control; and third, that a teacher's identity is constituted in relation to the emotional rules in the context in which she/he teaches. The contribution of a poststructuralist perspective in research on teacher emotion is discussed and analyzed.