SEPA Direct Debit (SDD) is a payment scheme within the Single Euro Payments Area (SEPA) that facilitates bank-to-bank euro transactions for regular payments like subscriptions and bills. It allows merchants to automate payment collection, providing benefits such as lower transaction costs, predictable revenue, and greater control over payment processes. The guide explains the distinctions between SDD core and business variants, emphasizes the importance of mandates for authorization, and outlines the operational framework within the SEPA network encompassing 35 countries.