The Hebrew Scriptures sometimes claim that there is only one God, and sometimes that Yahweh is the greatest among many gods. Things get even more confusing in the New Testament, where Jesus and the Holy Ghost are also referred to as God. The concept of the "Holy Trinity" was created to address this contradiction, but the Father, Son, and Holy Ghost continue to divide Christians today.
Unto thee it was shewed, that thou mightest know that the LORD he is God; there is none else beside him. Deuteronomy 4:35
The LORD he is God in heaven above, and upon the earth beneath: there is none else. Deuteronomy 4:39
Hear, O Israel: The Lord our God is one Lord. Deuteronomy 6:4
See now that I, even I, am he, and there is no god with me. Deuteronomy 32:39
The LORD, he is the God; the LORD, he is the God. 1 Kings 18:39
I am he: before me there was no God formed, neither shall there be after me. Isaiah 43:10
I am the LORD, and there is none else ... There is none beside me. I am the LORD, and there is none else. Isaiah 44:8
I am the Lord, and there is none else, there is no God beside me. Isaiah 45:5-6
There is no God else beside me ... There is none beside me. Isaiah 45:21
I am God, and there is none else: I am God, and there is none like me. Isaiah 46:9
The Lord our God is one Lord. Mark 12:29
There is one God; and there is none other but he. Mark 12:32
That they might know thee the only true God. John 17:3
But to us there is but one God, the Father, of whom are all things, and we in him. 1 Corinthians 8:6
In the book of Genesis, God used a plural pronoun to refer to himself (herself, itself, or themselves), implying that there is more than one god up there.
And God said, let us make man in our image. Genesis 1:26
And the Lord God said, Behold, then man is become as one of us, to know good and evil. Genesis 3:22
Let us go down, and there confound their language. Genesis 11:7
The Old Testament God is a "god of gods" who is worshiped by the other gods..
For the LORD your God is God of gods, and Lord of lords. Deuteronomy 10:17
Worship him, all ye gods. Psalm 97:7
O give thanks unto the God of gods. Psalm 136:2
No other god is like him.
Among the gods there is none like unto thee, O Lord. Psalm 86:8
He is better than the other gods.
Who is like unto thee, O LORD, among the gods? Exodus 15:11
Now I know that the LORD is greater than all gods. Exodus 18:11
Thou shalt have no other gods before me. ... Thou shalt not bow down thyself to them, nor serve them. Exodus 20:3-5
What God is there in heaven or in earth, that can do according to thy works? Deuteronomy 3:24
Great is our God above all gods. 2 Chronicles 2:5
Our Lord is above all gods. Psalm 135:5
The other gods will die someday.
The gods that have not made the heavens and the earth, even they shall perish from the earth, and from under these heavens. Jeremiah 10:11
The Hebrew God judges the other gods.
And against all the gods of Egypt I will execute judgment. Exodus 12:12
Upon their gods also the LORD executed judgments. Numbers 33:4
God standeth in the congregation of the mighty, he judgeth among the gods. Psalm 82:1
And will punish them.
I will punish the multitude of No, and Pharaoh, and Egypt, with their gods. Jeremiah 46:25
The Lord will be terrible to them: for he will famish all the gods of the earth. Zephaniah 2:11
He is a jealous God (whose name is Jealous). So he forbids us to "go after" or worship any of his competitors.
For thou shalt worship no other god: for the LORD, whose name is Jealous, is a jealous God. Exodus 34:14
Ye shall not go after other gods, of the gods of the people which are round about you; (For the LORD thy God is a jealous God among you.) Deuteronomy 6:14-15
Thou shalt not ... go after other gods to serve them. Deuteronomy 28:14
If you give God glory, he'll go easy on you and all your other gods.
Ye shall give glory unto the God of Israel: peradventure he will lighten his hand from off you, and from off your gods. 1 Samuel 6:5
And go not after other gods to serve them, and to worship them, and provoke me not to anger with the works of your hands; and I will do you no hurt. Jeremiah 25:6
But you must fear God more than all the other gods.
The Lord ... is to be feared above all gods. 1 Chronicles 16:25
For the Lord ... is to be feared above all gods. Psalm 96:4
Don't sacrfifice to any of the other gods. (Or God will kill you.)
He that sacrificeth unto any god, save unto the LORD only, he shall be utterly destroyed. Exodus 22:20
Don't put any of the other gods before him.
Thou shalt have none other gods before me. Deuteronomy 5:7
Don't make a covenant with them.
Thou shalt make no covenant with them, nor with their gods. Exodus 23:32
Don't burn incense to them.
I will utter my judgments against them ... who have forsaken me, and have burned incense unto other gods. Jeremiah 1:16
Or even mention their names.
Make no mention of the name of other gods, neither let it be heard out of thy mouth. Exodus 23:13
Put away your father's gods.
Fear the Lord ... and put away the gods which your fathers served. Joshua 24:14
And stay away from the god named Chemosh.
Wilt not thou possess that which Chemosh thy god giveth thee to possess? Judges 11:24
But don't revile the other gods.
Thou shalt not revile the gods. Exodus 22:28
Other people served other gods (as did Abraham's father Terah).
Your fathers dwelt on the other side of the flood in old time, even Terah, the father of Abraham, and the father of Nachor: and they served other gods. Joshua 24:2
And a witch once saw gods going up to heaven.
And the king said unto her, Be not afraid: for what sawest thou? And the woman said unto Saul, I saw gods ascending out of the earth. 1 Samuel 28:13
Always remember that people are gods too. (Jesus used this when he was accused of making himself a god.)
I have said, Ye are gods. Psalm 82:6
The Jews answered him, saying, For a good work we stone thee not; but for blasphemy; and because that thou, being a man, makest thyself God. Jesus answered them, Is it not written in your law, I said, Ye are gods? John 10:33-34
And the three gods in heaven are really only one god. (Don't worry about this one too much. It's a mystery.)
For there are three that bear record in heaven, the Father, the Word, and the Holy Ghost: and these three are one. 1 John 5:7