MicroRNAs (miRNAs) are a set of small, non-protein-coding RNAs that regulate gene expression at the post-transcriptional level. Maturation of miRNAs comprises several regulated steps resulting in approximately 22-nucleotide single-stranded mature miRNAs. Regulation of miRNA expression can occur both at the transcriptional level and at the post-transcriptional level during miRNA processing. Recent studies have elucidated specific aspects of the well-regulated nature of miRNA processing involving various regulatory proteins, editing of miRNA transcripts, and cellular location. In addition, single nucleotide polymorphisms in miRNA genes can also affect the processing efficiency of primary miRNA transcripts. In this review we present an overview of the currently known regulatory pathways of miRNA processing and provide a basis to understand how aberrant miRNA processing may arise and may be involved in pathophysiological conditions such as cancer.