Negotiation is a frequent phenomenon in everyday life. Whenever a person needs another person to solve their problems, their intertwining goals and preferences should be adjusted through negotiation. From this recurrent demand of dealing with negotiation, we constantly seek ways to improve it. One of the ways is by learning and assessing strategic behavior in negotiation. Starting from this objective, we systematically reviewed 1,490 articles to build a comprehensive outlook on negotiation behavior research progress. We use five systems of observation level to categorize the articles included in this study that are: (1) intrapersonal system, (2) interpersonal system, (3) group system, (4) organizational system, and (5) virtual system. The result showed us that the research landscape has progressed toward the development of automated negotiating agents besides observing human negotiators exclusively. We also see the emerging interplay between systems of observation level