In this review, current knowledge and ideas regarding several important functional-, structural-, and sequence-related aspects of microRNAs (miRNAs) are summarized. The current research on structural and functional aspects of miRNAs is rapidly growing, and new information appears regularly. Well-established information from literature useful for researchers working in this area has been compiled in this work. Although details of the methodology have not been elaborated, the outline should be useful for a broad and general understanding. The current information is highly interdisciplinary including molecular biology and bioinformatics; we have tried to bring both sides together. Little is known about the 3-D structure of miRNAs and its significance. miRNAs are usually active in conjunction with some proteins, and the complex is responsible for the intended task. Little information is available in the literature about the protein–miRNA interactions and their nature and properties. Nonetheless, we believe that the review will be useful to both bioinformaticians and molecular biologists.