THE LORD WAS SPEAKING TO THE ANGELS
I'll beg to differ with the previous poster. This is not the Trinity speaking to Himself, as too many mistakenly believe; rather, this is The Lord speaking to the host of heaven, also known as the Divine Council. This is God's assembly, His heavenly family, His entourage, called "bene elohim" (sons of God) in Hebrew. This concept is found throughout ancient rabbinic tradition and is preserved in the Hebrew bible in places like this:
1God has taken his place in the divine council; in
the midst of the gods he holds judgment:
6I said, “You are gods,
sons of the Most High, all of you; 7nevertheless, like men you shall die, and fall like any prince.”a
5Let the heavens praise your wonders, O LORD, your faithfulness in
the assembly of the holy ones! 6For who in the skies can be compared to the LORD? Who among the heavenly beings is like the LORD, 7God
greatly to be feared in the council of the holy ones, and awesome
above all who are around him? 8O LORD God of hosts, who is mighty as
you are, O LORD, with your faithfulness all around you?
In the Book of Job, it becomes clear that it was the "sons of God" called "the morning stars" who were with Him in at the creation:
4“Where were you when I laid the foundation of the earth? Tell me, if
you have understanding. 5Who determined its measurements—surely you
know! Or who stretched the line upon it? 6On what were its bases sunk,
or who laid its cornerstone, 7when the morning stars sang together and
all the sons of God shouted for joy?
Notice that they were with him when He laid the foundation of the Earth, and they were also with Him when He made Adam. In fact, when He had finished making Man, and had given him dominion over all that He had made, one of the angels had a question:
5For unto the angels hath he not put in subjection the
world to come, whereof we speak. 6But one in a certain place
testified, saying, What is man, that thou art mindful of him? or the
son of man, that thou visitest him? 7Thou madest him a little lower
than the angels; thou crownedst him with glory and honour, and didst
set him over the works of thy hands: 8Thou hast put all things in
subjection under his feet.
So, it should be clear that God was speaking to angels by now, but in case you still have doubts, consider what the Jewish rabbis taught and believed on this verse:
"Let us make man: From here we learn the humility of the Holy One,
blessed be He. Since man was created in the likeness of the angels,
and they would envy him, he consulted them. And when He judges kings,
He consults with His Heavenly household, for so we find regarding
Ahab, that Micah said to him, (I Kings 22:19): 'I saw the Lord seated
on His throne, and all the host of heaven were standing by Him, on His
right and on His left.' Now do 'left' or 'right' apply to Him ?! But
rather, [the passage means that] these [angels] were standing on the
right to defend, and these [angels] were standing on the left to
prosecute. Likewise, (Dan. 4:14): 'By the decree of the destructive
angels is the matter, and by the word of the holy ones is the edict.'
Here too, He took counsel with His heavenly household. He said to
them, 'Among the heavenly beings, there are some in My likeness. If
there are none in My likeness among the earthly beings, there will be
envy among the creatures of the Creation.'” - [from Tanchuma, Shemoth
18; Gen. Rabbah 8:11, 14:13]
"Let us make man: Even though they [the
angels] did not assist Him in His creation, and there is an
opportunity for the heretics to rebel (to misconstrue the plural as a
basis for their heresies), Scripture did not hesitate to teach proper
conduct and the trait of humility, that a great person should consult
with and receive permission from a smaller one. Had it been written:
'I shall make man,' we would not have learned that He was speaking to His tribunal, but to Himself. And the refutation to the heretics
is written alongside it [i. e., in the following verse:]'And God
created (וַיִּבְרָא) ,' and it does not say,'and they created
וַיִּבְרְאוּ.'” - [from Gen. Rabbah 8:9]
This rabbinic tradition is fleshed out in the Targum Pseudo-Jonathan version of this story:
"And the Lord said to the angels that ministered before Him, who had
been created in the second day of the creation of the world, Let Us
make man in Our image, in Our likeness..." - Gen. 1:26 (Targum
You may wonder why English bibles say "God," if this is true. The answer is that for a long time scholars misunderstood the meaning of the word "Elohim." If you study the passage in Hebrew, you'll note that in Genesis One "Elohim" is speaking, but in Genesis 2 "Yahweh" talks with Adam. This has been grounds for criticism by scoffers who claim that scripture is teaching two different creation accounts by two different deities. But, the truth is that the term "Elohim" includes Yahweh, but is not exclusive to Yahweh. Angels are also "Elohim." Today, we would simply say "Spirits."
I hope this helps.
For further study on this subject, I would recommend Dr. Michael Heiser's (resident scholar at LOGOS Bible Software, and Ph.D. in Hebrew and Semitic Languages) recently released book which goes into depth on this topic, and many others like it. It's called "The Unseen Realm."
You can find out more about the book here.