This chapter explores the fundamental geometry of circles, beginning with their presence in nature and ancient art before transitioning into formal mathematical principles. It defines a circle as a locus of points equidistant from a center on a two-dimensional plane and introduces essential terminology such as radius, chord, and diameter. Through various theorems and activities, the source details the symmetrical properties of circles and the geometric relationships between chords, including how they subtend angles at the center and how their lengths relate to their distance from the center. Finally, the text explains the construction of a circumcircle through three non-collinear points, illustrating the unique relationship between triangles and the circles that enclose them.