diff --git a/website/docs/cli/commands/plan.html.md b/website/docs/cli/commands/plan.html.md
index 03847cdf8..ce4e6e77a 100644
--- a/website/docs/cli/commands/plan.html.md
+++ b/website/docs/cli/commands/plan.html.md
@@ -176,7 +176,9 @@ the previous section, are also available with the same meanings on
 * `-var 'NAME=VALUE` - Sets a value for a single
   [input variable](/docs/language/values/variables.html) declared in the
   root module of the configuration. Use this option multiple times to set
-  more than one variable.
+  more than one variable. For more information see
+  [Input Variables on the Command Line](#input-variables-on-the-command-line),
+  below.
 
 * `-var-file=FILENAME` - Sets values for potentially many
   [input variables](/docs/language/values/variables.html) declared in the
@@ -189,6 +191,79 @@ module, aside from the `-var` and `-var-file` options. For more information,
 see
 [Assigning Values to Root Module Variables](/docs/language/values/variables.html#assigning-values-to-root-module-variables).
 
+### Input Variables on the Command Line
+
+You can use the `-var` command line option to specify values for
+[input variables](/docs/language/values/variables.html) declared in your
+root module.
+
+However, to do so will require writing a command line that is parsable both
+by your chosen command line shell _and_ Terraform, which can be complicated
+for expressions involving lots of quotes and escape sequences. In most cases
+we recommend using the `-var-file` option instead, and write your actual values
+in a separate file so that Terraform can parse them directly, rather than
+interpreting the result of your shell's parsing.
+
+To use `-var` on a Unix-style shell on a system like Linux or macOS we
+recommend writing the option argument in single quotes `'` to ensure the
+shell will interpret the value literally:
+
+```
+terraform plan -var 'name=value'
+```
+
+If your intended value also includes a single quote then you'll still need to
+escape that for correct interpretation by your shell, which also requires
+temporarily ending the quoted sequence so that the backslash escape character
+will be significant:
+
+```
+terraform plan -var 'name=va'\''lue'
+```
+
+When using Terraform on Windows, we recommend using the Windows Command Prompt
+(`cmd.exe`). When you pass a variable value to Terraform from the Windows
+Command Prompt, use double quotes `"` around the argument:
+
+```
+terraform plan -var "name=value"
+```
+
+If your intended value includes literal double quotes then you'll need to
+escape those with a backslash:
+
+```
+terraform plan -var "name=va\"lue"
+```
+
+PowerShell on Windows cannot correctly pass literal quotes to external programs,
+so we do not recommend using Terraform with PowerShell when you are on Windows.
+Use Windows Command Prompt instead.
+
+The appropriate syntax for writing the variable value is different depending
+on the variable's [type constraint](/docs/language/expressions/type-constraints.html).
+The primitive types `string`, `number`, and `bool` all expect a direct string
+value with no special punctuation except that required by your shell, as
+shown in the above examples. For all other type constraints, including list,
+map, and set types and the special `any` keyword, you must write a valid
+Terraform language expression representing the value, and write any necessary
+quoting or escape characters to ensure it will pass through your shell
+literally to Terraform. For example, for a `list(string)` type constraint:
+
+```
+# Unix-style shell
+terraform plan -var 'name=["a", "b", "c"]'
+
+# Windows Command Prompt (do not use PowerShell on Windows)
+terraform plan -var "name=[\"a\", \"b\", \"c\"]"
+```
+
+Similar constraints apply when setting input variables using environment
+variables. For more information on the various methods for setting root module
+input variables, see
+[Assigning Values to Root Module Variables](/docs/language/values/variables.html#assigning-values-to-root-module-variables).
+
+
 ### Resource Targeting
 
 > **Hands-on:** Try the [Target resources](https://learn.hashicorp.com/tutorials/terraform/resource-targeting?in=terraform/state&utm_source=WEBSITE&utm_medium=WEB_IO&utm_offer=ARTICLE_PAGE&utm_content=DOCS) tutorial on HashiCorp Learn.
diff --git a/website/docs/language/values/variables.html.md b/website/docs/language/values/variables.html.md
index f25f79aef..bad454533 100644
--- a/website/docs/language/values/variables.html.md
+++ b/website/docs/language/values/variables.html.md
@@ -349,7 +349,13 @@ terraform apply -var='image_id_list=["ami-abc123","ami-def456"]' -var="instance_
 terraform apply -var='image_id_map={"us-east-1":"ami-abc123","us-east-2":"ami-def456"}'
 ```
 
-The `-var` option can be used any number of times in a single command.
+The above examples show appropriate syntax for Unix-style shells, such as on
+Linux or macOS. For more information on shell quoting, including additional
+examples for Windows Command Prompt, see
+[Input Variables on the Command Line](/docs/cli/commands/plan.html#input-variables-on-the-command-line).
+
+You can use the `-var` option multiple times in a single command to set several
+different variables.
 
 <a id="variable-files"></a>
 
@@ -424,10 +430,11 @@ to assign complex-typed values, like lists and maps.
 
 Some special rules apply to the `-var` command line option and to environment
 variables. For convenience, Terraform defaults to interpreting `-var` and
-environment variable values as literal strings, which do not need to be quoted:
+environment variable values as literal strings, which need only shell quoting,
+and no special quoting for Terraform. For example, in a Unix-style shell:
 
 ```
-$ export TF_VAR_image_id=ami-abc123
+$ export TF_VAR_image_id='ami-abc123'
 ```
 
 However, if a root module variable uses a [type constraint](#type-constraints)
@@ -442,6 +449,9 @@ $ export TF_VAR_availability_zone_names='["us-west-1b","us-west-1d"]'
 
 For readability, and to avoid the need to worry about shell escaping, we
 recommend always setting complex variable values via variable definitions files.
+For more information on quoting and escaping for `-var` arguments,
+see
+[Input Variables on the Command Line](/docs/cli/commands/plan.html#input-variables-on-the-command-line).
 
 ### Values for Undeclared Variables