  Non-abelian gauge theories in the Higgs phase admit a startling variety of
BPS solitons. These include domain walls, vortex strings, confined monopoles
threaded on vortex strings, vortex strings ending on domain walls, monopoles
threaded on strings ending on domain walls, and more. After presenting a
self-contained review of these objects, including several new results on the
dynamics of domain walls, we go on to examine the possible interactions of
solitons of various types. We point out the existence of a classical binding
energy when the string ends on the domain wall which can be thought of as a BPS
boojum with negative mass. We present an index theorem for domain walls in
non-abelian gauge theories. We also answer questions such as: Which strings can
end on which walls? What happens when monopoles pass through domain walls? What
happens when domain walls pass through each other?
