This paper aims to fill the gap in the literature regarding business-to-business (B2B) cooperation agreements between hotels and airlines, providing the readers with insights regarding the airline market segment in the hotels" customer portfolio management and their benefits for both parties. Literature review includes legislation issues, operations management and customer service management process, as a catalyst for these agreements. A hidden tourism business sector is also presented and refers to intermediaries that often handle such agreements. Hotels and airlines are tourism businesses and cooperating bodies aiming at high quality customer service and travel experience optimization. This dimension is not met in the relevant literature and therefore, this paper contributes to the theory with business insights of such B2B cooperation environment. Empirical methodology includes a primary survey with questionnaires distributed in the five-star hotel units of Athens, aiming to investigate their agreements with the airlines operating from Athens International Airport. The results highlight the background, the conditions and the benefits that both hotels and airlines gain from such business-to-business contracts and are used to evaluate airline market segment for the hotel industry, underlining its contribution in occupancy rates and revenues, as well as in seasonality mitigation, among others. beverage departments, mitigation of seasonality, etc. In the following sections the background of B2B environment between airlines and hotels is developed, the research question resulting from literature review gap, the research methodology and the primary survey details along with the findings and the conclusions. The way forward is suggested as well.