The ryanodine receptors (RyRs) are a family of Ca$^2+$ release
channels found on intracellular Ca$^2+$ storage/release organelles.
The RyR channels are ubiquitously expressed in many types of cells
and participate in a variety of important Ca$^2+$ signaling phenomena
(neurotransmission, secretion, etc.). In striated muscle, the RyR
channels represent the primary pathway for Ca$^2+$ release during
the excitation-contraction coupling process. In general, the signals
that activate the RyR channels are known (e.g., sarcolemmal Ca$^2+$
influx or depolarization), but the specific mechanisms involved are
still being debated. The signals that modulate and/or turn off the
RyR channels remain ambiguous and the mechanisms involved unclear.
Over the last decade, studies of RyR-mediated Ca$^2+$ release
have taken many forms and have steadily advanced our knowledge. This
robust field, however, is not without controversial ideas and contradictory
results. Controversies surrounding the complex Ca$^2+$ regulation
of single RyR channels receive particular attention here. In addition,
a large body of information is synthesized into a focused perspective
of single RyR channel function. The present status of the single
RyR channel field and its likely future directions are also discussed.