Heb. 6:1-3 Therefore, let us leave the elementary teachings about Christ and go on to maturity, not laying again the foundation of repentance from acts that lead to death, and of faith in God, instruction about baptisms, the laying on of hands, the resurrection of the dead, and eternal judgment. (emphasis added) 
Great Commission

Matt. 28:19 …Therefore, go and make disciples of all nations, baptizing them in the name of the Father, and of the Son, and of the Holy Spirit…

Acts 2:38 (Peter's sermon at Pentecost) …repent and be baptized, every one of you… (3,000 were that very day! {vs 41})

Mk.16:16 "Whoever believes and is baptized will be saved…but whoever does not believe will be condemned."

Notice, it doesn't say 'whoever does not believe and is not baptized will be condemned', only "…whoever does not believe." 

? Is baptism necessary for salvation?
(To understand the implications of that question, consider this scenario:  There were two soldiers during in WW II - one in North Africa, and one on Guadalcanel. On the night before battle each accepts Jesus. One is baptized because of availability of water, one not. Next morning each is killed in action. Is one saved because he was baptized and the other damned because no water was available? 

Acts 10:34 "…everyone who believes in Him receives forgiveness of sins."

Acts 13:39 "Through Him everyone who believes is justified…"

Acts 16:30-31 (In response to the question, "What must I do to be saved?") "…Believe in the Lord Jesus, and you will be saved…" (Notice however, that the jailer and his family were then baptized)

? If it is argued that baptism is in fact necessary for salvation why would Paul say in I Cor.1:14 "I am thankful that I did not baptize any of you except Crispos & Gaius."

Or why did he say in I Cor.1:17 "…for Christ did not send me to baptize…"?  Keep in mind that according to Acts 20:27 Paul preached the 'whole will of God.' 

Consider Apolllos, there is no record of his being rebaptized in Jesus' name, yet there is no question about his salvation. Acts 18:25 (Apollos) "Though he knew only the baptism of John…" see also vs 19 

Acts 17:34 (No record of baptism, but there is clearly a salvation experience) 

Acts 10:47 (Cornelius' friends) "Can anyone keep these people from being baptized with water? They have received the Holy Spirit just as we have." 

? How could it possibly be argued that these gentiles were baptized in the Holy Spirit before they were saved??? 

Considering the above Scriptures, it seems clear that water baptism is not in fact required for salvation; yet,  it also seems clear that to refuse to be baptized after your salvation experience would appear to be an act of rebellion. 

Examples of baptism in Acts alone: 

Acts 2:41 (Pentecost) 

Acts 9:18 (Paul) 

Acts 8:36-39 (Ethiopian eunuch) 

Acts 8:16 (Samaritans) 

Acts 10:48 (Cornelius & friends) 

Acts 16:15 (Lydia) 

Acts 18:8 (believers in Corinth) 

Acts 19:5 

? In whose name should we be baptized, 'Lord Jesus Christ' or 'Father, Son and Holy Spirit'? 

Matt.28:19 says 'Father, Son and Holy Spirit'

Act 8:16 said that the believers were baptized in the name of the 'Lord Jesus.'

Acts 10:48 says 'Jesus Christ' (KJV says 'Lord Jesus Christ')

Who is right? ANSWER: They both are!

When you baptize in the name of the 'Lord Jesus Christ,' the 

LORD is Father
JESUS is Son
CHRIST is Holy Spirit.
Therefore, when a new believer is baptized in the name of the Lord Jesus Christ, (s)he is also by definition being baptized in the name of  the Father, the Son and the Holy Spirit
? Eph. 4:4 speaks of 'one Lord, one faith and one baptism.' How then can there be a 'water baptism' and a 'baptism of the Holy Spirit' and a 'baptism of fire?' 
Isn't that 3 baptisms?

In this case the 'ONE Lord' is 'FATHER, SON & HOLY SPIRIT

The 'ONE faith' is PAST, PRESENT & FUTURE (see John 11:17-37 - Lazarus)

The 'ONE baptism' is also three parts:

Water - I Pe. 3:21, Matt.3:13 Acts 8:38 Acts 10:47 

Holy Spirit - Mk.1:8 Acts 1:5 Acts 11:16

Fire - Matt 3:11 Mk.10:38

? Does baptism have to be by immersion?
     What about sprinkling?

Greek word baptizo Strong's Concordance # 907 and used in Matt. 28:19 (see above) = 'from a derivation of #911;to make overwhelmed (ie. fully wet)'

#911 is bapto 'cover fully with a liquid'

Vine's Expository Dictionary of New Testament Words 'to dip'

Greek English Lexicon of the New Testament and Other Early Christian Literature by Walter Bauer says these words mean 'dip, immerse, dip oneself, wash, … also plunge, sink, drench, overwhelm…'

Finally, the Ethiopian eunuch stopped the chariot where there was enough water for baptism, something he would not have had to do if he were merely going to be sprinkled. Furthermore, Acts 8:39 specifically states that afterwards they 'came up out of the water.'

? What about baptizing children?
There is no recorded incident of a small child (someone not aware of the importance of their action) being baptized in the New Testament. Old Testament contains examples of a child being dedicated to God shortly after birth, as was Jesus, but this is not baptism.