Transferring Roms

Due to the nature/complexity of Copyright/Intellectual Property Rights Law, which differs significantly from Country to Country, ROMs cannot be provided with RetroPie and must be provided by the user. You should only have ROMs of games that you own.

There are three main methods of transferring roms:

USB

(ensure that your USB is formatted to FAT32 or NTFS)
first create a folder called retropie on your USB stick
plug it into the pi and wait for it to finish blinking
pull the USB out and plug it into a computer
add the roms to their respective folders (in the retropie/roms folder)
plug it back into the raspberry pi
wait for it to finish blinking
refresh emulationstation by choosing restart emulationstation from the start menu

see this video for reference:

SFTP (needs an active internet connection)

Wired (needs ethernet cable)
Wireless (needs wifi dongle) There are many SFTP programs out there, for windows many people use WinSCP for mac you can use something like Cyberduck

winscp

Default username: pi

Default Password: raspberry

You can also log in as root if you wish to change more files than just the roms, but you first need to enable the root password which is explained here

Samba-Shares (needs an active internet connection)

if on windows type \\retropie into the computer folder. You can also replace retropie with your Raspberry Pi's IP address

samba

if on MAC OS X open finder, select "Go" menu and "Connect to Server". Type smb://retropieand hit "Connect".

Transferring Roms