Bitters categories: Angostura (gentian-based, classic, used in Old Fashioned, Whiskey Sour, Manhattan). Peychaud's (anise-cherry, NOLA, Sazerac). Orange bitters (Regan's, Fee Brothers Orange, House) — used in Martini, Old Fashioned variants. Specialty/house bitters (chocolate, mole, lavender, celery) — selective use, treat as flavor accents not base. Bitters are non-alcoholic for legal purposes despite their ABV.