Let \(G(R)\) denote the group of all formal power series over a commutative ring \(R\) under formal substitution. The natural filtration on \(R[[x]]\) induces the filtration \(\{K_ n\}\) on \(G(R)\). The following “large” properties are derived: If \(R^+\) is torsionfree, then so is \(G(R)\). The groups \(G(R)/K_ n\) are nilpotent and \(\cap_{n}K_ n=1\). If \(R\) is a principal ideal domain of characteristic zero then any commuting elements of \(G(R)\) are powers of a common element. The elements \(z(1+3z)^{-1}\), \(z(1+(3z)^ 3)^{-1/3}\) generate a free nonabelian group. Also the structure of the lower central series of \(G(R)\) is determined.