"Commitment" vs. "dedication"

When used in the context of giving oneself wholly to a cause/course of action etc., there is no real difference.

One is used more than the other in common phrases, but that's about it. For example you would usually hear:

He was a dedicated police officer.

Rather than:

He was a committed police officer.

Though both are equally valid. Dedicated in this context gives the impression of more zealous, heroic commitment.

Commitment can also imply obligation:

"Where's John?" "He's got work commitments."

Meaning he is obliged to be elsewhere because he has committed himself to work.

I'd say there is little effective difference, and I'd disagree with Elendil that dedicated is somehow more heroic, however the ever-so-slight differences are:

• Committed suggests that one is bound or obligated; perhaps one has made a pledge
• Dedicated suggest that one is devoted, but without there being a formal commitment.

In essence, once suggests a possibly-voluntary obligation and the other suggested a wholly-voluntary devotion, but in most everyday use, the terms are synonymous.

Commitment is about one’s obligation while dedication is about one’s passion in the performance of the obligation.