  In this lecture note we focus our attention to quantum dot systems where
exotic strongly correlated behavior develops due to the presence of orbital or
charge degrees of freedom. After giving a concise overview of the theory of
transport and Kondo effect through a single electron transistor, we discuss how
SU(4) Kondo effect develops in dots having orbitally degenerate states and in
double dot systems, and then study the singlet-triplet transition in lateral
quantum dots. Charge fluctuations and Matveev's mapping to the two-channel
Kondo model in the vicinity of charge degeneracy point are also discussed.
