Organizations have to cope with uncertainty in strategic decision making. Therefore concepts such as heuristics and simple rules firms use in making fast and frugal strategic decisions are gaining increasing attention in strategic management research. Yet, despite the importance of heuristics in strategic decision making, little is known how they actually function. Based on a longitudinal qualitative study of decision making under uncertainty we elaborate a more complex understanding of simple rules. First we show that strategic decisions consist of three basic elements: if/then rules, rule patterns and emotional handling. Secondly we reveal that firms develop generalizable rule patterns which follow a sequential order of inter-linked rules. Based on our study, we propose the concept of organizational heuristics, which are organizational rule patterns that enable a fast and frugal processing and evaluation of information in strategic decision making. Introducing the framework of organizational heuristics enables us to better understand and capture the complex reasoning process of firms in strategy processes. Finally our study contributes to the organizational learning literature by providing us with a better understanding of the way how different experience origins interact in simplification processes.