This study is the first to offer a comprehensive overview of Parmigianino’s enigmatic painting of The Madonna of the Long Neck in the Uffizi Gallery. It expands previous formalistic discussions to treat the subject in terms of iconography, semiotics, studio practice, and art theory. It is argued that the painting is not merely an example of mannerist extravagance, but that the Virgin in her extraordinary distension can be explained by a litany in Ecclesiasticus, with her enlargement read as a signifier of her mercy (Misericordia). Parmigianino’s panel is interpreted as an Immaculate Conception. Because the magisterium had not fully defined the belief as dogma, the theological debate confused the artist and his contemporaries, but also gave them flexibility in their depictions of this abstract doctrine. The painting is situated with others of the subject from Leonardo and Giovanni Bellini to Federico Barocci and El Greco. The subject’s genesis as a theological exercise is traced through the artist’s drawings. Illus.