NumericQ tests whether an object is a numeric quantity:

In most cases, NumericQ[expr] gives True whenever N[expr] yields an explicit number:

An object is numeric if all its constituents are numeric:

Some parts of the expression are numeric:

The system symbols that represent numerical constants:

Some of the system symbols with the NumericFunction attribute:

Any combination of these functions with numeric arguments will be numeric:

In most cases, N[e] will not be a number since it is improbable that the arguments are correct:

Test if a matrix consists of numeric entries:

Define a function that only evaluates when its argument is numeric:

Define a function that has a special case for numeric arguments:

If NumberQ[x] is True, then NumericQ[x] is also True:

When f has the NumericFunction attribute, then f[args] is numeric when args are numeric:

NumericQ will give True for numerical expressions that may produce real or complex values:

Only one of these two values is real:

Use RealValuedNumericQ to test for numeric expressions that are real valued.

NumericQ[e] does not always imply that N[e] will yield a number:

This can also happen when the arguments for the function are given incorrectly: