Vienna has been internationally known for its social housing system for over a century, with a large share of the population living in rent-controlled or subsidized apartments. The model emerged in response to severe housing shortages caused by industrialization, the collapse of the Austro-Hungarian Empire, and mass migration to the city, which had left workers living in overcrowded and unsanitary conditions. After 1919, under Socialist leadership, Vienna began large-scale municipal housing construction during the interwar period known as “Red Vienna.” Extensive housing complexes such as the Karl-Marx-Hof were built as self-contained urban quarters with courtyards, social infrastructure, and affordable rents. Between 1923 and 1934, more than 60,000 apartments were constructed, complemented by smaller settlement projects. Today, Vienna owns around 220,000 municipal apartments—about a quarter of the city’s housing stock—many of them historically protected. Alongside non-profit housing developers and renovation programs like the “Gentle Urban Renewal,” about 60% of Vienna’s population lives in affordable housing. While eligibility rules are sometimes criticized, Vienna emphasizes social mixing to avoid segregation. Land provision through the Wohnfonds Wien and quality control via developer competitions remain central, though rising construction costs make further development increasingly challenging.