The Missionaries of St. John the Baptist or Baptistines was a Roman Catholic religious institute dedicated to Saint John the Baptist.
The congregation of missionary priests of St. John the Baptist, called Baptistines, was founded by a Genoese, Domenico Olivieri. He began by uniting several priests with himself for the evangelization of the people of the towns and countryside. His plan of forming from this company an association the members of which should devote their time especially to missions was encouraged by Cardinal Spinola and the scheme afterwards received the approbation of Pope Benedict XIV. The pope confirmed the new congregation in his Brief of 23 September 1755, and placed it under the control of the Cardinal Prefect of the Propaganda.
The institute had a house and an oratory at Rome near the church of St. Isidoro, and the members held missions in the different churches of the city and in the surrounding countryside. As the Congregation wished to employ them in distant missions, a number of them were sent to Bulgaria, Macedonia, and China; some became bishops. Foreign missions did not absorb all their activity, for a number were employed in the service of the Church in Italy, two, Imperiali and Spinelli becoming cardinals. The only vows imposed by the founder were those of continuance in the congregation and readiness to go to missions to which the members should be sent by the Congregation. Olivieri died at Genoa on 13 June 1766. The society disappeared during the troubles which overwhelmed Italy at the end of the eighteenth century.