The string theory description of BPS states in D-brane world-volume field t
heories may undergo transitions from open strings to string webs, as well a
s between different string webs, as one moves in the field theory moduli sp
ace. These transitions are driven by the string creation phenomenon. We dem
onstrate such transitions in the D3-brane realization of N = 2 SU(2) Super-
Yang-Mills theory. (C) 1998 Elsevier Science B.V.