ittekimasu 行ってきます

In Japanese, ittekimasu 行ってきます, meaning literally "to go and come back," is an expression used to say goodbye by someone leaving home to go school, work, etc. Whoever remains home bids farewell saying itterasshai 行ってらっしゃい.

When the person returns, they say tadaima ただいま, and are greeted by okaeri おかえり.

Meaning

The phrase itte-kimasu 行ってきます is composed by two verbs:

• iku
  行く
  To go.
• itte is the te-form of iku.
• kimasu
  来ます
  To come.

The non-polite variant would be:

• itte-kuru
  行ってくる
  To go and come back.

The phrase literary says what the person will do. If they'll leave for school, for example, they'll go to school, then they'll come back later: itte-kuru.

The phrase doesn't necessarily mean "to leave home and then come back." It means "to go somewhere, and then come back," so it can also be used by someone leaving other places, like a classroom.

• {chotto mi ni} itte kuru
  ちょっと見に行ってくる
  [I] will go {see for a bit}, then come back.

Someone bidding farewell with itterasshai is literally saying:

• itte-koi
  行って来い
  Go and come back.
  (meireikei 命令形, "imperative form.")

This ~te-kuru ～てくる can be used in various other phrases related to going somewhere and coming back later.

• dekakeru
  出かける
  To leave home to go somewhere.
• dekakete-kuru
  出かけてくる
  To leave home to go somewhere, and then come back.
• kau
  買う
  To buy.
• katte-kuru
  買ってくる
  To go buy something, then come back.