This chapter focuses on ways in which attitudes are assessed. There is a wide diversity in attitude assessment practices; an appropriate way to examine these practices is through the lens of the COI (cognition, observation, and interpretation) assessment triangle as reported in Knowing What Students Know (Pellegrino, Chudowsky, & Glaser, 2001). The usage of the COI assessment triangle provides a unique approach to analyzing current attitude-based assessments and assessment design. We provide an overview of existing research methods and instruments used to assess attitudes followed by a brief discussion about the meaning of “attitudes towards science.” We focus the COI analysis on two articles and discuss assessment strategies, assessment design, ways in which results are interpreted, and implications for assessment practices in the future.