When and where was Philippians written? Philippians is attributed to a Roman provenance ca. 62 CE by most english commentators (see Bockmuehl; Witherington; O'Brien; Fee; Silva etc.) yet many continental commentators are open to an Ephesian setting ca. 55-57 (e.g. Gnilka; Muller, etc.). Mark Goodacre in his 2008 SBL paper on Dating the Crucial Sources in Early Christianity gave Philippians and Philemon a question mark in regards to their place in a Pauline chronology which reflects the indeterminate nature of the evidence. More recently, though, I've become convinced of the probability of an Ephesian provenance ca. 55-58 CE during an imprisonment in Ephesus for Paul's letter to the Philippians. In a nutshell, here are the best arguments:
(1) Most Pauline chronologists (e.g. Knox, Ludemann, Jewett, and Riesner) either posit or allow for the possibility of an Ephesian imprisonment (see 2 Cor. 1.8-11).
(2) Assuming the unity of the epistle to the Philippians (see John Reumann in AB for the alternative view), Philippians 3 stands out as including some polemical remarks against proselytizing opponents (3.2-9) and some anti-nominan behaviours (3.11-12, 18-19) which may reflect very recent debates in Galatia and Corinth and Paul is doing some preventative house keeping to make sure that another 'church' does not go the same route.
(3) The reference to the praetorium in Phil. 1.13 does not necessarily correspond to the imperial residence in Rome because (a) would the emperor really house accused criminals from the east in his own residence?; and (b) praetorium can mean simply 'head quarters' in places outside of Rome.
(4) There are a number of similarities in language and ethos between Philippians and Philemon. Francis Watson has shown the similarities in language between both epistles and we can note that these two epistles also look forwad to Paul's imminent release from detention. There are too many journeys implied by the movement of Paul's co-workers (Ephaphras, Onesimus, Tychicus, John Mark) back and forth between Paul's locale and the Lycus Valley for Philemon to have been written from Rome which is over 1000 miles away, hence, Ephesus is a more likely setting for Philemon. Thus, if Philemon and Philippians are co-temporous, they were probably written from Ephesus.
(5) Paul's intent to send Timothy to the Philippians in Phil. 2.19 probably corresponds to the sending of Timothy to Macedonia in Acts 19.22. There is no evidence, internal or external, that Timothy ever accompanied Paul to Rome (if the Pastorals are authentic or early post-Pauline then Timothy was definitely outside of Rome during Paul's Roman imprisonment).
(6) How does this pan out for Pauline chronology? If Philippians was written from Ephesus after Galatians and 1 Corinthians, then Paul probably composed it during ca. 55-56 not long after Timothy had returned from the visit to Corinth that Paul describes in 1 Cor. 4.17, 16.10-11 and after the tearful letter of 2 Cor. 2.1-4. Paul intends to send Timothy to Philippi (Phil. 2.19 = Acts 19.22) and to eventually visit himself (Phil. 2.24; 2 Cor. 2.12-13; = Acts 20.1).
See further:
Francis Watson, Paul, Judaism, and the Gentiles: Beyond the New Perspective (Grand Rapids, MI: Eerdmans, 2007).
Frank S. Thielman, 'Ephesus and the Literary Setting of Philippians,' in New Testament Greek and Exegesis: Essays in Honor of Gerald F. Hawthorne, eds. A. M. donaldson and T. B. Sailors (Grand Rapids, MI: Eerdmans, 2003), 205-25.