Answer
What is the difference between Booking.com and Expedia for hotels?
Booking.com and Expedia are the two largest OTAs serving independent hotels. Booking.com is European-headquartered (part of Booking Holdings), uses the agency model (you set the rate, OTA earns commission), and charges 15-18% commission for independents. Expedia is US-headquartered (part of Expedia Group), uses a merchant-model in many markets (Expedia bills the guest, remits net to property), and typically charges 18-25%. Both also offer packages (rooms + flight + car), but Expedia's packaging is stronger. Most independent hotels list on both to capture geographically distinct demand.
The agency vs merchant model
Booking.com operates on the agency model: the guest books a rate the property sets, pays the property directly at check-out (or via prepaid options the property opts into), and Booking.com invoices commission monthly. Expedia historically operated on the merchant model where Expedia took the payment and remitted net of commission to the property. Today both models coexist, with merchant becoming more common at Booking.com via Booking.com Payments and Expedia offering both.
Geographic strengths
Booking.com dominates in Europe, Latin America (excluding Brazil), Asia-Pacific outside Japan, and most of the Middle East. Expedia dominates in the US, has strong UK and Ireland presence, and partners with Trivago, Hotwire and Wotif in different markets. Both list in every major market, but the cost of acquisition through one versus the other shifts based on where the booking originated.
Package and TravelAds layer
Expedia's package layer (room + flight + car) drives 25-35% of Expedia hotel bookings in the US leisure market according to Expedia Group disclosures. Properties opted into Expedia TravelAds pay incremental commission for top-of-search placement. Booking.com's equivalent is Genius and Preferred Partner; both raise visibility in exchange for higher commission.