Turkish Airlines often provides the most direct service between Logan International Airport (BOS) and Istanbul Airport (IST), with full-service international amenities and generous checked baggage allowances on long-haul flights. European carriers like British Airways, Lufthansa, and KLM provide one-stop options through LHR, FRA, and AMS respectively—these can be cheaper and offer convenient connection times. Evaluate seat comfort, loyalty benefits, baggage rules, and change/cancellation policies when booking December travel. CTA: Compare fares and policies across Turkish Airlines and key European partners to determine the best choice for your Boston to Istanbul trip.