Critics often claim that we know nothing about Jesus outside of the New Testament. I believe this claim is often the result of assumption and not investigation.
What follows is a summary of the data we have regarding Jesus outside of the New Testament from non-Christian sources.
There exist 17 known non-Christian sources that were written within 100-150 years of Jesus life which is excellent for ancient history. 
They are as follows:
They are as follows:
Pliny the Younger
Other Jewish Sources
Other Gentile Sources
The Gospel of Truth
The Apocryphon of John
The Gospel of Thomas
The Treatise on Resurrection
Other Lost Works
Acts of Pontius Pilate- recorded as actual documents by Justin Martyr (ca. AD 150) and Tertullian (ca. AD 200). Both agree that it was an official document of Rome.
Phlegon- Phlegon’s work is not longer in existence and we depend on others for our information. 
What facts about Jesus do these ancient non-Christian sources report?
Here are just 12 of them:
1. Jesus lived during the time of Tiberius Caesar.
2. He lived a virtuous life.
3. He was a wonder-worker.
4. He had a brother named James.
5. He was acclaimed to be the Messiah.
6. He was crucified under Pontius Pilate.
7. He was crucified on the eve of the Jewish Passover.
8. Darkness and an earthquake occurred when he died.
9. His disciples believed he rose from the dead.
10. His disciples were willing to die for their belief.
11. Christianity spread rapidly as far as Rome.
12. His disciples denied the Roman gods and worshiped Jesus as God. 
Please note that these facts are completely consistent with what the New Testament documents report concerning Christ.
From these non-Christian sources, we know more than 60 facts of the life of Jesus from outside the New Testament.
For those interested in examining more of these facts, please see here.
For readers interested in exploring the historical evidence for Jesus more in-depth, I recommend Gary Habermas' The Historical Jesus and/or Mike Licona's The Resurrection of Jesus: A New Historiographical Approach.
To view the other common objections we have dealt with, go here.
Courage and Godspeed,
1. Dr. Gary Habermas, Lecture: The Historical Jesus, Biola University.
2. Dr. Gary Habermas, The Historical Jesus, p. 187-228.
3. Norman Geisler and Frank Turek, I Don’t have Enough Faith to be an Atheist, p. 222-223.