  Time-distance helioseismology and related techniques show great promise for
probing the structure and dynamics of the subphotospheric layers of the Sun.
Indeed time-distance helioseismology has already been applied to make
inferences about structures and flows under sunspots and active regions, to map
long-lived convective flow patterns, and so on. Yet certainly there are still
many inadequacies in the current approaches and, as the data get better and the
questions we seek to address get more subtle, methods that were previously
regarded as adequate are no longer acceptable. Here we give a short and partial
description of outstanding problems in local helioseismology, using
time-distance helioseismology as a guiding example.
