Journal ArticleThe literature on the topic of health information systems (HISs) is reviewed in this paper. Specifically, the paper reviews the literature on (i) the theoretical concept of HISs (The What), (ii) the rationale, purposes, and importance (The Why), and (iii) the operationalization of the HISs (The How). For this systematic review, we searched Research Gate, Science Direct, Google Scholar, JSTOR, ProQuest, Scopus, PMC, BMJ, PubMed, and published documents by World Health Organization (WHO). Only 35 articles out of 1,400 articles identified were included in the study depending on the 3 contextualised questions i.e., the what, why, and how of the HISs. Literature published between 1960 and 2021 were considered in the review as the concept of HIS was introduced in the 1960s, excluding literature published before the 1960s and non-English publications. Generally, the HISs is one of the six pillars that make up a strong health system, designed to collect, process, store and manage health information. The main goal of the HISs is to deliver quality services. The importance of these systems includes quick access to medical records, sharing of patient information, reducing paperwork, reducing medical errors, improve the quality of care. Therefore, there is a great need to promote this concept, taking into account its rationale, purposes, and importance of it in the health care system.