These lecture notes provide an overview of the renormalization group
(RG) as a successful framework to understand critical phenomena above
the upper critical dimension d_{uc}duc.
After an introduction to the scaling picture of continuous phase
transitions, we discuss the apparent failure of the Gaussian fixed point
to capture scaling for Landau mean-field theory, which should hold in
the thermodynamic limit above d_{uc}duc.
We recount how Fisher’s dangerous-irrelevant-variable formalism applied
to thermodynamic functions partially repairs the situation but at the
expense of hyperscaling and finite-size scaling, both of which were,
until recently, believed not to apply above
d_{uc}duc.
We recall limitations of various attempts to match the RG with
analytical and numerical results for Ising systems. We explain how the
extension of dangerous irrelevancy to the correlation sector is key to
marrying the above concepts into a comprehensive RG scaling picture that
renders hyperscaling and finite-size scaling valid in all dimensions.
We collect what we believe is the current status of the theory,
including some new insights and results. This paper is in grateful
memory of Michael Fisher who introduced many of the concepts discussed
and who, half a century later, contributed to their advancement.