In this thesis, we consider some aspects of noncommutative classical invariant theory, i.e., noncommutative invariants of the classical group SL(2, k). We develop a symbolic method for invariants and covariants, and we use the method to compule some invariant algebras. The subspace ar~ of the noncommutative invariant algebra J'~ consisting of homogeneous elements of degree m has the structure of a module over the symmetric group S,,. We find the explicit decomposition into irreducible modules. As a consequence, we obtain the Hilbert series of the commutative classical invariant algebras. The Cayley---Sylvester theorem and the Hermite reciprocity law are studied in some detail. We consider a new power series //(I'd, t) whose coefficients are the number of irreducible S,,-modules in the decomposition of J'~, and show that it is rational. Finally, we develop some analogues of all this for covariants.