  We develop a general framework to analyze the two important and much
discussed questions concerning (a) `orbital' and `spin' angular momentum
carried by light and (b) the paraxial approximation of the free Maxwell system
both in the classical as well as quantum domains. After formulating the
classical free Maxwell system in the transverse gauge in terms of complex
analytical signals we derive expressions for the constants of motion associated
with its Poincar\'{e} symmetry. In particular, we show that the constant of
motion corresponding to the total angular momentum ${\bf J}$ naturally splits
into an `orbital' part ${\bf L}$ and a `spin' part ${\bf S}$ each of which is a
constant of motion in its own right. We then proceed to discuss quantization of
the free Maxwell system and construct the operators generating the Poincar\'{e}
group in the quantum context and analyze their algebraic properties and find
that while the quantum counterparts $\hat{{\bf L}}$ and $\hat{{\bf S}}$ of
${\bf L}$ and ${\bf S}$ go over into bona fide observables, they fail to
satisfy the angular momentum algebra precluding the possibility of their
interpretation as `orbital' and `spin' operators at the classical level. On the
other hand $\hat{{\bf J}}=\hat{{\bf L}}+ \hat{{\bf S}}$ does satisfy the
angular momentum algebra and together with $\hat{{\bf S}}$ generates the group
$E(3)$. We then present an analysis of single photon states, paraxial
quantization both in the scalar as well as vector cases, single photon states
in the paraxial regime. All along a close connection is maintained with the
Hilbert space $\mathcal{M}$ that arises in the classical context thereby
providing a bridge between classical and quantum descriptions of radiation
fields.
