Author:

The letter has been accepted, from the earliest of times, as from the apostle Paul. The letter is quoted by many early church fathers including Clement, Ignatius, and Barnabas.
The style of the letter has some differences from other letters of Paul, including words that are not used elsewhere, but still contains a large number of Pauline touches. Colossians is firmly established in the canon of the Church.

Occasion:

Paul is in prison, probably in Rome and has received a visit from the pastor of the Colossian congregation. It seems Epaphras, the pastor had come to consult Paul on a heresy causing problems in the church. Scholars are divided as to which of the times in prison this letter was written. Cases can be made for the time in prison in Ephesus, Caesarea, and Rome, most leaning toward the time in Rome.

Place:

Colossae was the smallest of three cities in the Lycus Valley in present-day Turkey. The other two cities were Laodicea and Hierapolis, each of which also had Christian congregations. The city had previously been the most important of the three from its textile industry but had, at the time of the writing been reduced in importance to such an extent that the great Persian road which used to run through the city then ran through Laodicea.

People:

There would have been a very diverse population in Colossae at the time of Paul's writing. There was a large Jewish contingent, settled there in 213 BCE; still a minority, but a large one. The closeness to the highway exposed the people to a wide variety of travelers bringing a wide variety of ideas.
The people of the congregation in Colossae were likely more Gentile than Jew since Paul uses descriptions and terminology that would be more appropriate to this type of believer. Whatever the heresy is that Paul was countering, it set the Jewish believers and the Gentile believers at odds over food restrictions, holy days, and circumcision.