S Curve can refer to the following:

• S Curve (art), an art term for a sinuous body position, noted in ancient marble sculpture
• Sigmoid function, a mathematical function that produces a sigmoid curve or a curve having an "S" shape
• S-Curve Records, a record label
• Reverse curve, a type of horizontal curve

Many natural processes, including those of complex system learning curves, exhibit a progression from small beginnings that accelerates and approaches a climax over time. When a detailed description is lacking, a sigmoid function is often used. A sigmoid curve is produced by a mathematical function having an "S" shape. Often, sigmoid function refers to the special case of the logistic function shown at right and defined by the formula

Another example is the Gompertz curve. It is used in modeling systems that saturate at large values of t. Another example is the ogee curve as used in the spillway of some dams. A wide variety of sigmoid functions have been used as the activation function of artificial neurons, including the logistic function and tanh(x).