A collection of selected papers written by the information theorist and "brain physicist," most of which were presented to various scientific conferences in the 1950s and 1960s. Most of this collection concerns MacKay's abiding preoccupation with information as represented and utilized in the brain and exchanged between human beings, rather than as formalized in logical patterns of elementary propositions.
As someone with no knowledge of information theory or even maths, I was pleasantly surprised at how accessible MacKay made this. Some of the thought is a bit dated, written as it was in a time of switchboard technology, but is nonetheless very helpful in reframing information around meaning in a rigorous way through a series of short lectures.
In terms of situating early theories of information into a cohesive picture and outlining lots of the open questions information scientists, and systems researchers might still explore, there's a lot here. This is probably one of the most organized introductions to information and its possibilities I've read as a theory book. While perhaps some of the conversations here are dated relative to what Information studies are about now, this isn't to say new ideas can't come from this book. I noticed ideas here that frame large sections of my academic interests into information in a consistent way and further them into a potential set of questions worthy of exploration. My only criticism here is that it is such a shame that theories of information focused so regularly on formal structures of language rather than other sorts of information.