In this chapter, we describe two self-report user study methods that can be used in the field to understand behavior over longer time periods (typically one week or more, and sometimes one month or more). We begin with diary studies, where participants keep a log (text, voice notes, photos, etc.) about their thoughts or experiences (eg, the times and places that they exhibited a certain behavior). We then discuss the experience sampling method (ESM), where participants respond to brief questionnaires at specific times or contexts. These two methods share many things in common, and they can be used to collect similar types of data (including qualitative and/or quantitative). As mentioned in earlier chapters, diary studies and experience sampling form the backbone of many field studies in the Human-Computer Interaction (HCI) domain. They allow researchers to hear directly from the participants in a study while the study is in progress and reduce the reliance on recall from other common self-report methods, such as traditional interviews and surveys. They help researchers to more reliably understand how and why a participant performs certain actions at specific times under naturalistic circumstances as well as how attitudes or behaviors change over time in a way that a single interview, survey, or quantitative logs cannot fully address.