Ischemic stroke is an etiologically heterogenous disorder. Classification of ischemic stroke etiology into categories with discrete phenotypic, therapeutic, and prognostic features is indispensible to generate consistent information from stroke research. In addition, a functional classification of stroke etiology is critical to ensure unity among physicians and comparability among studies. There are two major approaches to etiologic classification in stroke. Phenotypic systems define subtypes by providing a summary of abnormal test results organized in major etiologic categories. Causative systems, on the other hand, integrate diagnostic test results and clinical stroke features through a decision making process to identify the most likely etiology. This article intends to provide a review on important historical, theoretical, and practical aspects of etiologic stroke classification and current classification systems