Carl Philipp Emanuel Bach (1714-1788) published his Versuch über die wahre Art das Clavier zu spielen in 1753 and 1762. It was the most important essay on keyboard performance practice of the mid-eighteenth century. The publication of this book also made C. P. E. Bach the most influential keyboard pedagogue of the eighteenth century. The last chapter of the Versüch, titled ¡§Improvisation¡¨, explains his concepts of ¡§Freie Fantasia¡¨ and provides suggestions for performing the fantasia. C. P. E. Bach points out that Freie Fantasia is a kind of composition in which the performer has much freedom for improvising and for expressing his emotion. This thesis is divided into three sections, excluding the introduction and the conclusion. The first section discusses the development of the fantasia before the eighteenth century. It explores the change of styles and compositional technique of the fantasia from the sixteenth to the eighteenth century. The second part includes an introduction of the life of C. P. E. Bach, his style of composition, technique of improvisation and how he applies his improvisational techniques in his fantasia. The third part provides the definition of ¡§Freie Fantasia¡¨, discusses the influences of J. S. Bach¡¦s Chromatic Fantasia and Fugue in D Minor on him, and elaborates on the characteristics of the Freie Fantasia, including the recitative style, meter-free and formal structure, virtuosic passages, bold modulations, and the use of contrasting materials. Examples are also provided in this part.