Even though workplace conditions worldwide are subject to local and international laws, labor conditions in global supply chains have continuously raised human rights concerns. In response to societal pressure, multinationals have taken on a certain degree of responsibility regarding workplace conditions in supplier factories, notably by adopting codes of conduct. Investigating the impact of this self‐regulatory policy, scholars have examined whether and how codes shape labor conditions at the production level, but the results of their empirical studies diverge and sometimes contradict. To bring clarity to the field and gain an overarching understanding of the impact of codes, this literature review analyzes the question of their effectiveness as examined in 33 scientific papers gathered via a systematic selection of empirical studies. The review shows that supplier codes are not deemed unanimously and evenly effective by scholars and often fail to improve labor conditions. However, a range of factors are identified that facilitate the implementation of codes and ensure its effectiveness. This article develops a taxonomy of these factors and intends to contribute to understanding codes' decoupling and recoupling processes by investigating the gap between codes provisions and their intended outcome: the improvement of labor practices in global supply chains.