Vesicles constitute an interesting morphology formed by self-aggregating
amphiphilic molecules. They exhibit a rich structural variety and are of interest
both from a fundamental point of view (for studying closed bilayer systems) and
from a practical point of view (whenever one is interested in the encapsulation of
active molecules). In many circumstances vesicular structures have to be formed
by external forces, but of great interest are amphiphilic systems, where they
form spontaneously. Here the question arises of whether this means that
they are also thermodynamically stable structures, which at least in some
systems appears to be the case. If such vesicles are well defined in size,
it is possible to pack them densely and thereby form vesicle gels that
possess highly elastic properties even for relatively low volume fractions of
amphiphile. Conditions for the formation and the microstructure of such
vesicle gels have been studied in some detail for the case of unilamellar
vesicles. Another important and topical issue is the dynamics of vesicle
formation/breakdown, as the understanding of the transition process will open the
way to a deeper understanding of their stability and also allow controlling of
the structures formed, by means of their formation processes. Significant
progress in the study of the transformation processes has been achieved,
in particular by means of time-resolved scattering experiments.