I want to transfer $20,000 to a friend from my US bank account to His. Will there be any tax implications for him? Is there a limit to how much can I transfer?

[Carl]

You'll have to ask your bank or whatever service (western union maybe?) if they have a limit. Now for tax purposes, if this is a loan that you are NOT charging interest on, you have nothing to report, since it will be *presumably* paid back.
However, if you are *giving* it to the friend as a gift that never has to be paid back, then any gifts of more than $14K given in a tax year require the giver of said gift to file a gift tax return with the IRS. There will be no taxes paid on it. But the filing is still required. TurboTax does not deal with the gift tax return at all. You'll have to see a CPA for that.
For the recipient of a gift, they report absolutely nothing to anybody. Any reporting requirements are on the giver of the gift - not the recipient.

[SweetieJean]

Just be aware of potential money laundering concerns.

[SweetieJean]

What is the reason for the transfer?

[SweetieJean]

and are either of you foreign nationals?

[Opus 17]

Gifts are not taxable to the giver or the recipient.

If the transfer is a loan, you don't owe tax now but will owe tax on the interest if you are repaid with interest.

All transactions over $10,000 are automatically reported to the IRS.  No tax may be owed, but if you are doing something you shouldn't be (such as moving proceeds from illegal activity, or disguising a payment for work performed as a gift), realize there will be a record of the transaction that could be investigated if there was cause to do so.

[Rus86]

Is it for each transaction $10000? Or for year ?

[Critter-3]

Each transaction of $10K or more requires a paper trail per banking regulations. 

[NCperson]

not aware of that requirement.... it is true that BANKS are required by law to report any transaction that exceeds $10,000 to the IRS per the Currency and Foreign Transactions Reporting Act...... but where is the requirement that the person who makes the deposit or withdrawal have a paper trail?  Yes, it would be prudent to be able to support where the $10,000 came from or went to if asked by governmental authorities, but not confident there is any legal requirement to maintain such records. 

[Critter-3]

If you are ever audited and they review your banking transactions and you don't have some kind of records of where this money came from then the IRS can consider it all unreported income and it would be your responsibility to prove them wrong.  Income audits  is how they catch people who work under the table or have illegal income. 

[tagteam]

https://www.fincen.gov/sites/default/files/shared/CTRPamphlet.pdf

Cash or coin transactions over $10,000.

@Critter-3 is absolutely correct, though; in the (admittedly unlikely) event of an income audit, the taxpayer needs to establish the source of the funds and, if that is not possible, the IRS will consider those amounts taxable income.