  We study 1/2 BPS domain walls, 1/2 BPS flux tubes (strings) and their 1/4 BPS
junctions. We consider the simplest example of N=2 Abelian gauge theory with
two charged matter hypermultiplets which contains all of the above-listed
extended objects. In particular, we focus on string-wall junctions (boojums)
and calculate their energy. It turns out to be logarithmically divergent in the
infrared domain. We compute this energy first in the (2+1)-dimensional
effective theory on the domain wall and then, as a check, obtain the same
result from the point of view of (3+1)-dimensional bulk theory. Next, we study
interactions of boojums considering all possible geometries of string-wall
junctions and directions of the string magnetic fluxes.
