The paper deals with the defense of Vinkovci municipality in 1991. The goals, purpose and structure of the work are explained in the introductory chapter. The introductory chapter is followed by a chapter in which the methodology of the work is explained and an overview of the used literature and analyzed sources is given. The work is primarily based on an impressive number of documents from the Operational Headquarters of the MUP of the Republic of Croatia from the Croatian State Archives and on available ICTY documents, the Vinkovci Crisis Headquarters fund from the Croatian Homeland War Memorial Documentation Center and documents available to the author from the 109th and 3rd Brigades. In the next chapter, the geographical and demographic characteristics of Vinkovci municipality are presented. As the end of the introductory chapters, there is a chapter in which an overview of the participants and warring parties is presented. The central part of the paper deals chronologically with the development of the security and military situation in the period from the democratic changes to the Sarajevo Agreement, while the largest part of the paper analyzes in detail the military operations in the period from the end of summer to the beginning of winter of 1991. At the end of the paper, the consequences of the war are analyzed, as well as the effectiveness of the warring parties.