  The dissolution time (t_dis) of clusters in a tidal field does not scale with
the ``classical'' expression for the relaxation time. First, the scaling with
N, and hence cluster mass, is shallower due to the finite escape time of stars.
Secondly, the cluster half-mass radius is of little importance. This is due to
a balance between the relative tidal field strength and internal relaxation,
which have an opposite effect on t_dis, but of similar magnitude. When external
perturbations, such as encounters with giant molecular clouds (GMC) are
important, t_dis for an individual cluster depends strongly on radius. The mean
dissolution time for a population of clusters, however, scales in the same way
with mass as for the tidal field, due to the weak dependence of radius on mass.
The environmental parameters that determine t_dis are the tidal field strength
and the density of molecular gas. We compare the empirically derived t_dis of
clusters in six galaxies to theoretical predictions and argue that encounters
with GMCs are the dominant destruction mechanism. Finally, we discuss a number
of pitfalls in the derivations of t_dis from observations, such as
incompleteness, with the cluster system of the SMC as particular example.
