References

Introduction to metric entropy.

Entropy theory for endomorphisms of probability spaces goes back to Kolmogorov on one hand and to Shannon on the other. A pleasant introduction that resists the injuries of time is the monograph

Most modern monographs in ergodic theory include a section on entropy. A point which we did not touch is the Shannon-Breiman-McMillan Theorem. For a short account that includes the a proof of Doob's martingale theorem see

For an historical survey filled with personal recollections:

Furstenberg on noncommuting random products.

Non commutative ergodic theorems