The Wolfram Language normally takes any expression it is given, and evaluates it as far as possible. But built into the Wolfram Language is a collection of flexible primitives that allow finer control over the process of evaluation in cases where it is needed.

Evaluation Control for Complete Expressions

Hold — hold an expression unevaluated

HoldForm, HoldCompleteForm — display an expression in unevaluated form

Defer — display unevaluated, but evaluate if given as Wolfram Language input

Evaluation Control for Function Arguments

HoldAll, HoldFirst, HoldRest — attributes for specifying held function arguments

Evaluate — immediately evaluate a function argument

Unevaluated — pass a function argument unevaluated

More Detailed Control

ReleaseHold — release hold constructs

HoldComplete  ▪  HoldPattern  ▪  HoldAllComplete  ▪  SequenceHold  ▪  Update

NHoldAll, NHoldFirst, NHoldRest — prevent numerical evaluation of arguments

Manipulating Unevaluated Expressions

With — insert variable values without evaluation

Extract — extract numbered parts without evaluation

Keys, Values — extract keys and values without evaluation

ReplaceAll(/.)  ▪  ReplacePart  ▪  Delete  ▪  Position

ToString, ToExpression — convert to and from string form

Global Evaluation Control

$IterationLimit  ▪  $RecursionLimit  ▪  TerminatedEvaluation

Resource Constraints

TimeConstrained  ▪  MemoryConstrained

Evaluation in Notebooks

Dynamic  ▪  Refresh  ▪  Evaluator

Inactivated Expressions

Inactivate — inactivate all parts of an expression, printing them in gray

Activate — re-activate part of an expression

Inactive — wrapper to put around every symbol in an inactive expression

IgnoringInactive — pattern match ignore inactive wrappers

DisableFormatting — prevent the formatting of held expressions