introduction materials to the actor model?

I am looking for some introductions to the actor model. I don’t mind books in specific programming languages, as long as they don’t distract away or restrict the presentation of the model

Is this a good one?

Actors: A Model of Concurrent Computation in Distributed Systems (MIT Press), by Gul Agha, 1986

I am uncertain because

• it is a PhD dissertation which might be for things that were experimental and then found useless, and
• it was in 1986 and I am not sure how much the model has changed.

Thanks.