Circles
- Annulus
- Apollonian Gasket
- Apollonian Network
- Apollonius Circle
- Auxiliary Circle
- Borromean Rings
- Butterfly Theorem
- Casey's Theorem
- Central Circle
- Circle
- Circle Catacaustic
- Circle-Circle Intersection
- Circle-Circle Tangents
- Circle Covering by Arcs
- Circle Cycle
- Circle Discriminant
- Circle Division by Chords
- Circle Division by Lines
- Circle-Ellipse Intersection
- Circle Evolute
- Circle Inverse Curve
- Circle Inversion
- Circle Involute
- Circle Involute Pedal Curve
- Circle-Line Intersection
- Circle Line Picking
- Circle Negative Pedal Curve
- Circle of Curvature
- Circle Orthotomic
- Circle Packing
- Circle Pedal Curve
- Circle-Point Midpoint Theorem
- Circle Point Picking
- Circle Power
- Circle Radial Curve
- Circle Strophoid
- Circle Tangent Line
- Circle Triangle Picking
- Circumcenter
- Circumcenter of Mass
- Circumference
- Clifford's Circle Theorem
- Coaxal Circles
- Coaxal System
- Coaxaloid System
- Coin Paradox
- Concentric Circles
- Concyclic
- Congruent Incircles Point
- Coxeter's Loxodromic Sequence of Tangent Circles
- d'Alembert's Theorem
- Descartes Circle Theorem
- Diameter
- Eccentric
- Eight-Point Circle Theorem
- Ellipse Pedal Curve
- Enclosing Circle
- Excenter
- Excenter-Excenter Circle
- Excosine Circle
- Exradius
- Extangent
- Extent
- Eyeball Theorem
- Flower of Life
- Ford Circle
- Four Coins Problem
- Gauss's Circle Problem
- Goat Problem
- Great Circle
- Hart Circle
- Hart's Theorem
- Homologous Points
- Hyperbola Pedal Curve
- Incenter
- Intangent
- Inversion Circle
- Isodynamic Circles
- Isodynamic Points
- Japanese Theorem
- Jiang Zemin's Problem
- Johnson Circles
- Johnson Midpoint
- Johnson's Theorem
- Jung's Theorem
- Kinney's Set
- Kűrschák's Theorem
- Limiting Point
- Line-Circle Intersection
- Lune
- Malfatti Circles
- Malfatti's Problem
- McCay Circles
- Midcircle
- Minimal Enclosing Circle
- Miquel Five Circles Theorem
- Miquel's Pentagram Theorem
- Monge's Circle Theorem
- Monge's Problem
- N-Cluster
- Nine Circles Theorem
- Nine-Point Circle
- Orthogonal Circles
- Osculating Circle
- Pappus Chain
- Parabola Negative Pedal Curve
- Pizza Theorem
- Point Circle
- Poncelet's Closure Theorem
- Poncelet's Coaxal Theorem
- Poncelet's Porism
- Poncelet Transverse
- Purser's Theorem
- Radical Circle
- Radius
- Rigid Circle Packing
- Rounded Rectangle
- Sangaku Problem
- Schinzel Circle
- Schinzel's Theorem
- Schoute Coaxal System
- Seed of Life
- Semicircle
- Semicircumference
- Seven Circles Theorem
- Similarity Point
- Similitude Circle
- Six Circles Theorem
- Small Circle
- Squircle
- Stadium
- Steiner Chain
- Steiner's Porism
- Symmetric Points
- Tangency Theorem
- Tangent Circles
- Thales' Theorem
- Triquetra
- Uniform Circular Motion
- Unit Circle
- Unit Disk
- Unit Disk Integral
- Villarceau Circles
- Weill's Theorem
- Yin-Yang