Can I paint directly over painted wood?

Yes, you can paint directly over painted wood in many cases if old paint is in good condition, but you need proper preparation for good adhesion and durable finish. If painted wood is clean, not peeling, cracking, or glossy, you can paint directly after cleaning surface with soap and water to remove grease and dust, lightly sanding with fine sandpaper to degloss and create key for new paint to grip, wiping dust, and then applying new paint, ideally two coats. If old paint is oil based and you want to use water based latex, you must sand and apply bonding primer first, otherwise latex will peel. If old painted wood is glossy, you must sand to dull gloss or use bonding primer, otherwise new paint will not stick. If old paint is peeling, chipping, or flaking, you must scrape loose paint, sand edges smooth, fill holes, and prime bare spots, not paint directly over failing paint. If old paint has stains or dark color and you are going light, use primer first to block stains and improve coverage. For wood trim, doors, or furniture, light sanding and primer gives best result. So yes you can paint directly over painted wood if it is sound, clean, and dull, but for best adhesion and longevity, light sanding and primer is recommended, especially for glossy or oil based old paint.