This report summarizes information presented at the 2015 Keystone Symposium on "MicroRNAs and Noncoding RNAs in Cancer." Nearly two decades after the discovery of the first miRNA, the role of noncoding RNAs in developmental processes and the mechanisms behind their dysregulation in cancer has been steadily elucidated. Excitingly, miRNAs have begun making their way into the clinic to combat diseases such as hepatitis C and various forms of cancer. Therefore, at this Keystone meeting, novel findings were presented that enhance our view on how small and long noncoding RNAs control developmental timing and oncogenic processes. Recurring themes included (i) how miRNAs can be differentially processed, degraded, and regulated by ribonucleoprotein complexes, (ii) how particular miRNA genetic networks that control developmental process, when disrupted, can result in cancer disease, (iii) the technologies available to therapeutically deliver RNA to combat diseases such as cancer, and (iv) the elucidation of the mechanism of actions for long noncoding RNAs, currently a poorly understood class of noncoding RNA. During the meeting, there was an emphasis on presenting unpublished findings, and the breadth of topics covered reflected how inescapable the influence of noncoding RNAs is in development and cancer.