**Gerbes and D-branes**

In the hierachy of geometrical objects gerbes are next to
line bundles. They are chacterized by an integral closed 3-form.
This is in string theory represented by the so called H-field.
Gerbe modules are generalizations of vector bundles and appear naturally
in string theory as D-branes. Their stable equivalence classes can be
used to define twisted K-theory. In the case of the Wess-Zumino-Witten
model the (equivariant) twisted K-theory is closely related to the Verlinde
algebra.

*Branislav Jurčo*