From Apostles to Bishops is an excellent survey of the early development of the episcopacy. Francis A. Sullivan takes a cautious, critical-historical approach to the data we have, and avoids the common assertions and arguments from silence that are often made by historians and theologians who discuss this topic. Sullivan is a Catholic, but this is not a work of apologetics; he spends more time criticizing reductive Catholic arguments than he does rebutting protestants.
Sullivan concludes that there is good evidence for collegial, presbyteral leadership in both the new testament and other 1st century Christian writings such as Clement's letter to the Corinthians or the Didache. He concludes that the rapid and universal development of the mono-episcopacy (one ruling bishop per city) in the mid-2nd century was a valid example of the holy spirit guiding the Church into truth through consensus, akin to the Church's 2nd century selection of Biblical texts such as the four gospels. In other words, the mono-episcopacy was not always an institution in the church, but its very early development reflects a continuation of the trajectory set by the apostles; Sullivan argues that the episcopacy and it's accompanying authority is a divine institution in the same way that the canon of scripture is divinely instituted. This is a thesis that will challenge Catholic/Orthodox Christians who have an overly-simplistic view of early Christianity, and it will also challenge those protestants who haven't thought much about why the early church, decades after the New Testament was penned, suddenly unanimously decided to organize themselves under bishops.
There are a couple of faults in Sullivan's work that I found (and these are more pet peeves than substantive problems). First, he has a tendency to rely heavily on the consensus of "the scholars." There are numerous instances where he either cites Raymond Brown as an authority or just says "the majority of modern scholars hold __" (without ever citing any of these scholars or their arguments). This keeps the book brief but also weakens several of his historical points by making them assertive appeals to authority. In-depth endnotes or some kind of appendix summary of the scholarly arguments that Sullivan was leaning on would have improved things.
Also, Sullivan does this weird critical-scholar psychoanalysis that I think leads to really weak inferences. You see this more often in biblical scholarship where people will psycho-analyze Paul or the author 1 Peter or whatever, but Sullivan does it with Ignatius of Antioch. He argues (apparently with the support of many scholars, who are not cited), that when Ignatius of Antioch left on his journey to be martyred in Rome, Antioch was obviously in the midst of a serious schism. Why? Not because we have any documentary evidence of schism in Antioch, or because Ignatius says anything about it in his 7 letters that he wrote to other churches. The reason Antioch must have been in schism is that Ignatius writes with an self-deprecating tone (e.g. referring to himself as barely worthy of the office of Bishop) and because his constant, unambiguous calls to unity under each local Bishop must indicate that he felt like the episcopacy wasn't as strong of an institution as he wished it was. This feels like motivated, circular reasoning - modern critical scholars, who frequently seem to want to argue that everything in Christianity developed well after the apostles, would like to argue that the episcopacy as it existed throughout the middle ages didn't really become widespread until the 3rd century. Ignatius contradicts this, as he writes 6 letters to Bishops (who he names in the letters) at the beginning of the 2nd century and uses the strongest language possible to argue that Churches are not Churches unless they are gathered under their bishop, and that Bishops "all around the world" hold authority. Therefore, because we all know the episcopacy wasn't well established anywhere until the 3rd century (remember, all the modern scholars say so), Ignatius can't mean what he's saying and must be a tortured soul who is disappointed in the schism he left behind in Antioch. As a result of his inner turmoil, he's over-inflating or inventing a novel emphasis on ecclesial unity under the bishop. I think this is goofy, and it would be easier to just admit that by the early 2nd century, the episcopacy was common in some areas (especially in Antioch...), and some theologians such as Ignatius had been reflecting on the theological implications of the episcopacy for some time, since Ignatius' theology seems quite developed. It's fine to say "Ignatius might have exaggerated a bit, since we have other evidence that seems to disagree with what he said," but it feels quite odd to psychoanalyze an author who has been dead for 1900 years and draw historical conclusions (that happen to be the opposite of what the author in question wrote) from this psychoanalysis.
Other than those quibbles, this is a great book for anybody (Protestant/Catholic/Atheist/whatever) who is interested in the early development of christian ecclesiology. This is a solid work of history!!