The government-issued international travel document required for any tour crossing borders. Tour managers need to track passport expiry per crew member; most countries require 6 months of validity remaining on entry. Dual-citizens may carry two passports and use whichever is more advantageous for each border (e.g., a US/UK dual citizen uses UK on entry to Schengen for visa-free travel, US on return). Track multiple passports per person if your roster includes dual-citizens.