thumb|Alessi's original project for the façade of Palazzo Marino, Milan, altered in the execution
Galeazzo Alessi (1512 – 30 December 1572) was an Italian architect from Perugia, known throughout Europe for his distinctive style based on his enthusiasm for ancient architecture. He studied drawing for civil and military architecture under the direction of Giovanni Battista Caporali.
For a number of years he lived in Genoa. He was involved in the lay-out of the streets and the restoration of the city walls, as well as being responsible for many of its impressive palazzi, now a part of the World Heritage List. Alessi displayed particular aptitude for organizing compositions on sloping sites.
- Saint-Georges Church, Périgueux, France His work can be found in many other Italian cities, including in Ferrara, Bologna, Naples and Milan, where he designed the facade of Santa Maria presso San Celso. With Vignola, he designed the Basilica of Santa Maria degli Angeli in Assisi, the seventh largest Christian church at the time. Elsewhere in Europe, he designed churches and palaces in France, Germany and Flanders.
- Porta del Molo (Porta Siberia), inserted in the city walls
- Cupola of St. Lawrence Cathedral