Alekhine's Defence – Main Line arises after 1.e4 Nf6 2.e5 Nd5. ECO code: B02.

This is the standard continuation, forming the basis for all main Alekhine variations. The knight retreats to d5, inviting White to gain further space with c4. The critical choice for White is between 3.d4 (entering the Four Pawns Attack, Exchange, or Modern Variations after ...d6) and 3.c4 (the Two Pawns Attack, less common). Black aims to undermine and exploit the overextended centre.