This paper explores the dynamics of the highly fluid Italian legislative pa
rty system. It uses the same theoretical approach as the paper by Laver and
Kato (this issue) to explore the making and breaking of governments in Ita
ly following electoral reform. Under office-seeking motivational assumption
s, the electoral system provides incentives for parties to band together in
to cartels in order to fight elections, with the winning cartel forming a g
overnment coalition. Inter-electoral legislative party competition, however
, within a structure of permissive rules on the formation of legislative pa
rty groups, provides incentives for at least some members of the winning ca
rtel to defect. The facility with which legislative parties can split and c
ombine in Italy creates a highly dynamic decisive structure underpinning th
e making and breaking of governments. This cannot usefully be analysed with
traditional models that take parties as unitary actors and assume that the
party system is essentially fixed for the entire inter-electoral period. (
C) 2001 Elsevier Science Ltd. All rights reserved.