Universal multiplication on K-theory

In homotopy theory the existence of spectrum level ring structures
is an important question for theoretical and computations purposes.
We discuss the existence and uniqueness of these ring structure 
on algebraic and topological K-theory. Instead of using the 
classical approach with carefully chosen 'infinite loopspace 
machines' or obstruction theory our main tool will be the use 
of certain universal properties. This has the advantage of 
giving strong uniqueness results and also works in parametrized 
situations.