Christian apologetics is a verbal or written defense of the Bible and Christian faith. As Christians we are to contend for the faith by being ready to give answer for anyone who question about the hope within us.
Beloved, when I gave all diligence to write unto you of the common salvation, it was needful for me to write unto you, and exhort you that ye should earnestly contend for the faith which was once delivered unto the saints. For there are certain men crept in unawares, who were before of old ordained to this condemnation, ungodly men, turning the grace of our God into lasciviousness, and denying the only Lord God, and our Lord Jesus Christ. Jude 1:3-4
But sanctify the Lord God in your hearts: and be ready always to give an answer to every man that asketh you a reason of the hope that is in you with meekness and fear: Having a good conscience; that, whereas they speak evil of you, as of evildoers, they may be ashamed that falsely accuse your good conversation in Christ. 1 Peter 3:15-16
When preaching the gospel to the lost world you are bound to come into contact with people asking questions about Christianity. I put together a list of Christian apologetic websites. The sites below are some of the best I've visited and wanted to share with you.
Tekton Apologetics Ministries
Tekton Education and Apologetics Ministries of James Patrick Holding. Tekton has an apologetics encyclopedia answering Bible difficulties and Bible contradictions.
http://tektonics.org
Got Questions?
Do you have a question about God, Jesus, the Bible, or theology? GotQuestions.org offers fast and accurate answers to all your Bible Questions!
http://gotquestions.org
Christian Apologetics & Research Ministry
CARM is a Christian ministry dedicated to the glory of the Lord Jesus Christ and the promotion and defense of the Christian Gospel, Doctrine, and Theology. CARM analyzes religions such as Islam, Jehovah's Witnesses, Mormonism, Roman Catholicism, Universalism, Wicca, etc., and compares them to the Bible. Also analyzing secular ideas such as abortion, atheism, evolution, and relativism. In all of their analyses they use logic and evidence to defend Christianity and promote the truth of the Bible which is the inspired word of God.
http://carm.org
Christian Answers.Net
An index of answers to frequently-asked-questions about the Bible and Christian theology.
http://christiananswers.net/menu-at1.html
Christian Thinktank
A free, public website with over 6000 pages organized by questions and objections concerning Christianity and other topics.
http://christianthinktank.com
Apologetics Press
For more than 30 years Apologetics Press has published and disseminated materials for self study, group study, or evangelistic purposes. Topics range from evidences supporting the Christian Faith to highly controversial areas that challenge that Faith.
http://apologeticspress.org 
English (US) 
