Izquierda Castellana constituted a definitive movement in Madrid by the year 2002, as a section of Izquierda Comunera, which also included the organizations Unidad Popular Castellana, YESCA (formerly known as Juventudes Castellanas Revolucionarias), Mujeres Castellanas and the Círculo Castellano de Toledo. The Communist Party of the Castilian People (a section of the Communist Party of the Peoples of Spain in the autonomous region of Castilla y León) joined on as part of Izquierda Castellana, but later left the organization. Izquierda Castellana also supports various nationalist movements around the world, such as those in the Basque Country, Palestine or Ireland, emphasizing a democratic perspective and the sovereignty of the working class.
The goal of Izquierda Castellana is the attainment of what they call a united Castile, overcoming the current division of the Castilian "nation" between five autonomous regions (Cantabria, Castile and León, Madrid, La Rioja and Castile-La Mancha) and a comarca (Requena-Utiel in the Valencian Community). It emphasizes socialism, sovereignty and republicanism, principles it reaffirms each year on April 23, in a special ceremony in the municipality of Villalar de los Comuneros. This day is celebrated by Castilian nationalist organizations such as Izquierda Castellana and Tierra Comunera as the National Day of Castile, but officially it is the festivity of the autonomous region of Castile and León.