本文介绍了怪诞装饰的发展和变化，并尝试从中寻找怪诞观念变化的原因。古代怪诞装饰（grotesque ornament）在文艺复兴时期被再次发现并得到广泛传播。“怪诞”装饰被认为是“洞穴”（grotto）里的装饰是由于当时人们对古代遗迹的误解，它的实际起源应追溯到古代的壁画装饰。怪诞装饰并不符合古典审美要求，它的广泛流行刺激了文艺复兴艺术家们的想象力，也使他们回顾中世纪怪诞边饰。

在怪诞艺术和相关美学思想中，都存在怪诞和阿拉伯式两词混用的情况。本文通过探讨怪诞装饰与阿拉伯式装饰之间的关系，强调威尼斯-萨拉森纹样设计的影响，指出两词长期被用作同义词可能源于形式上的相似，十五世纪阿拉伯式装饰自威尼斯进入欧洲，其丰富繁复的特征对怪诞装饰的空间安排产生了影响。十八、十九世纪的怪诞装饰，以及怪诞观念的变化，尤其是在浪漫主义中，对哥特式艺术的复兴和推崇使人们把怪诞与崇高等观念联系起来。早期浪漫主义的美学著作中也常见以“阿拉伯式”指怪诞风格。

怪诞的历史并不局限在装饰艺术方面，漫画和版画的兴起和盛行也促使怪诞艺术的发展。在集中讨论怪诞及其边缘地位时，有提及中世纪文化对怪诞漫画的一些影响。本文最后一节简要地介绍了中国广州哥特式教堂的滴水嘴装饰。

There are four major attempts in this thesis. First, to explore the classical origin of grotesque ornament and its rediscovery and dissemination during the Renaissance, thus claiming that the etymology of "grotesque", originated from "grotto", is based on a false idea about the ancient site from which it had been discovered, and that the "grottesche" in Renaissance was in fact an imitation of the mural decoration in Roman houses. Second, to point out that two different styles of grotesque coexisted, classical and medieval, and to clarify the sources and impacts of each, laying particular stress on constrains given by decorative frames and linking structures. Third, to examine the relationship between “grotesque” and “arabesque”, stress particularly on the Venetian-Saracenic decoration. Formal resemblances might be one of the reasons that the two were used constantly as synonyms. Also, influenced by arabesque decorations, grotesque ornaments became dense and more complicated. Fourth, to discuss grotesque ornament in eighteenth- and nineteenth-centuries, noting that in the age of Romanticism, the grotesque had been attached to the concept of sublime by some Gothic Revivalists. History of the grotesque does not restrict itself in decorative arts. The rise of caricature and printmaking also gave force to the development of the grotesque. Focusing on the grotesque ornament and its marginal status, influence of medieval culture to caricature has been mentioned in the discussion of medieval grotesque. Finally, some lines have been written for a brief discussion of the decoration of Gothic cathedral in Guangzhou, China.