In this paper we derive decomposition results for the number of customers i
n polling systems under arbitrary (dynamic) polling order and service polic
ies. Furthermore, we obtain sharper decomposition results for both the numb
er of customers in the system and the waiting times under static polling po
licies. Our analysis, which is based on distributional laws, relaxes the Po
isson assumption that characterizes the polling systems literature. In part
icular, we obtain exact decomposition results for systems with either Mixed
Generalized Erlang (MGE) arrival processes, or asymptotically exact decomp
osition results for systems with general renewal arrival processes under he
avy traffic conditions. The derived decomposition results can be used to ob
tain the performance analysis of specific systems. As an example, we evalua
te the performance of gated Markovian polling systems operating under heavy
traffic conditions. We also provide numerical evidence that our heavy traf
fic analysis is very accurate even for moderate traffic.