At the core of the Wolfram Language is the foundational idea that everything—data, programs, formulas, graphics, documents—can be represented as symbolic expressions. And it is this unifying concept that underlies the Wolfram Language's symbolic programming paradigm, and makes possible much of the unique power of the Wolfram Language and the Wolfram System.

Expression Structure »

FullForm — the full form of an expression, without shortened syntax

TreeForm   ▪ Head   ▪ Length   ▪ Depth   ▪ Symbol   ▪ Construct   ▪ ...

Common General-Purpose Expression Types

List   ▪ Association   ▪ Dataset   ▪ Rule

Transforming Expressions »

expr/.rules — make replacements for any occurrence of a pattern in an expression

Applying Functions »

Map , Apply — map, apply a function at any level in any expression

Expression Testing »

SameQ (=== )  ▪ FreeQ   ▪ MemberQ   ▪ NumberQ   ▪ OrderedQ   ▪ ...

Parts of Expressions »

Part (..[[..]] ) — numbered parts of an expression, reset using =

Position   ▪ ReplacePart   ▪ MapAt   ▪ ReplaceAt   ▪ Delete   ▪ ...

Cases — find occurrences of a pattern in an expression

Structural Operations »

Flatten   ▪ Thread   ▪ Distribute   ▪ FlattenAt   ▪ Append   ▪ ...

Controlling Expression Evaluation »

Hold   ▪ Evaluate   ▪ HoldFirst   ▪ HoldAll   ▪ Inactive   ▪ ...

Raw Data Structures »

CreateDataStructure   ▪ DataStructure