Iteration is an essential element of software development processes. Software methodologies like agile and waterfall use the term ‘iteration’ in several different ways for improving either the quality or the functionality of the software. There are no studies, however, which have thoroughly analyzed and characterized these forms of iterations and their differences as they are enacted in organizations. In order to reveal these iterative forms we conducted a study of two mid-sized software development projects at a large global Fortune 100 corporation – one agile project and one waterfall project. Using advanced event sequence-analytic techniques based on detailed process data, our analysis reveals that agile and waterfall iterations differed in design and development phases due to different sources and types of iterations.