Massive and open online courses (MOOCs) satisfy learning needs from the particularities of their typologies (xMOOC, tMOOC, cMOOC, iMOOC, among others) even though their high dropout rate is still latent. Recent studies reaffirm engagement as an alternative to reduce dropout rates. The literature analyzed has not yet been able to systematize responses as to how to guarantee engagement in MOOCs and thus reduce their attrition rate. And, consistent with that question, are there still challenges for teachers in this area of educational technology? These answers motivated us to carry out this systematic review to determine how engagement has been studied to help reduce the attrition rate in MOOCs. Articles from journals indexed in Scopus or WoS were reviewed applying the PRISMA protocol. At the end of the protocol, it was defined to analyze 40 studies. The results reflect that the main variables are: the design of e-activities, intrinsic and extrinsic motivation, and communication between students. This paper confirms that the main challenges to guarantee engagement in MOOCs are individualized tutoring, interactivity, and feedback. Due to the scarcity of studies that analyze the variables in an integrated way, it is proposed as future work to determine what relationships exist between these variables that interfere with engagement and dropout in MOOCs.