  Biological systems are influenced by fluid mechanics at nearly all
spatiotemporal scales. This broad relevance of fluid mechanics to biology has
been increasingly appreciated by engineers and biologists alike, leading to
continued expansion of research in the field of biological fluid dynamics.
While this growth is exciting, it can present a barrier to researchers seeking
a concise introduction to key challenges and opportunities for progress in the
field. Rather than attempt a comprehensive review of the literature, this
article highlights a limited selection of classic and recent work. In addition
to motivating the study of biological fluid dynamics in general, the goal is to
identify both longstanding and emerging conceptual questions that can guide
future research. Answers to these fluid mechanics questions can lead to
breakthroughs in our ability to predict, diagnose, and correct biological
dysfunction, while also inspiring a host of new engineering technologies.
