identifying the citizens of a cell

Is there a way of identifying all the proteins active in a cell and how they interact with one another?

What is the perfect method of understanding intracellular protein-to-protein interaction? The best method so far lies in knock-outs/in experimentation, where mutation is induced. However, this method takes a longer time and even though the exact mechanism of interactions unknown.

What we need is a way of taking one cell and identifying the proteins involved, then tagging the proteins and observing how they interact with one another. The important question is HOW can this  be done??