This study extracts and reports notable findings on passive micromixers by conducting an exhaustive review of designs, their features, and mixing performance. The study has covered the relevant articles on passive micromixers published from 2010 to 2020. The analysis of filtered and selected articles sums up passive micromixers into four categories: designed inlets, designed mixing-channel, lamination-based, and flow obstacles-based. The prominent mixing channel categories identified in the study are split-and-recombine (SAR), convergent-divergent (C-D), and mixed (SAR, C-D, and others). Moreover, differences in mixing channel designs, number of inlets, and evaluation methods have been used in comparing the mixing performance of passive micromixers. The SAR and the obstacles-based micromixers were found to outperform the others. The designs covered in the present review show significant improvements in the mixing index. However, these studies were conducted in an isolated environment, and most of the time, their fabrication and device integration issues were ignored. The assortment and critical analysis of micromixers based on their design features and flow parameters will be helpful to researchers interested in designing new passive micromixers for microfluidic applications.