diff --git a/pkg/yqlib/doc/operators/string-operators.md b/pkg/yqlib/doc/operators/string-operators.md
index c9447a998a..47c3e3204e 100644
--- a/pkg/yqlib/doc/operators/string-operators.md
+++ b/pkg/yqlib/doc/operators/string-operators.md
@@ -49,6 +49,38 @@ Note that versions prior to 4.18 require the 'eval/e' command to be specified.&#
 `yq e <exp> <file>`
 {% endhint %}
 
+## To up (upper) case
+Works with unicode characters
+
+Given a sample.yml file of:
+```yaml
+água
+```
+then
+```bash
+yq 'upcase' sample.yml
+```
+will output
+```yaml
+ÁGUA
+```
+
+## To down (lower) case
+Works with unicode characters
+
+Given a sample.yml file of:
+```yaml
+ÁgUA
+```
+then
+```bash
+yq 'downcase' sample.yml
+```
+will output
+```yaml
+água
+```
+
 ## Join strings
 Given a sample.yml file of:
 ```yaml
diff --git a/pkg/yqlib/expression_tokeniser.go b/pkg/yqlib/expression_tokeniser.go
index ddd582d679..9f02453641 100644
--- a/pkg/yqlib/expression_tokeniser.go
+++ b/pkg/yqlib/expression_tokeniser.go
@@ -414,6 +414,12 @@ func initLexer() (*lex.Lexer, error) {
 	lexer.Add([]byte(`capture`), opToken(captureOpType))
 	lexer.Add([]byte(`test`), opToken(testOpType))
 
+	lexer.Add([]byte(`upcase`), opTokenWithPrefs(changeCaseOpType, nil, changeCasePrefs{ToUpperCase: true}))
+	lexer.Add([]byte(`ascii_upcase`), opTokenWithPrefs(changeCaseOpType, nil, changeCasePrefs{ToUpperCase: true}))
+
+	lexer.Add([]byte(`downcase`), opTokenWithPrefs(changeCaseOpType, nil, changeCasePrefs{ToUpperCase: false}))
+	lexer.Add([]byte(`ascii_downcase`), opTokenWithPrefs(changeCaseOpType, nil, changeCasePrefs{ToUpperCase: false}))
+
 	lexer.Add([]byte(`sort`), opToken(sortOpType))
 	lexer.Add([]byte(`sort_by`), opToken(sortByOpType))
 	lexer.Add([]byte(`reverse`), opToken(reverseOpType))
diff --git a/pkg/yqlib/lib.go b/pkg/yqlib/lib.go
index dd07d5c12a..0adc308633 100644
--- a/pkg/yqlib/lib.go
+++ b/pkg/yqlib/lib.go
@@ -125,13 +125,16 @@ var explodeOpType = &operationType{Type: "EXPLODE", NumArgs: 1, Precedence: 50,
 var sortByOpType = &operationType{Type: "SORT_BY", NumArgs: 1, Precedence: 50, Handler: sortByOperator}
 var reverseOpType = &operationType{Type: "REVERSE", NumArgs: 0, Precedence: 50, Handler: reverseOperator}
 var sortOpType = &operationType{Type: "SORT", NumArgs: 0, Precedence: 50, Handler: sortOperator}
+
 var sortKeysOpType = &operationType{Type: "SORT_KEYS", NumArgs: 1, Precedence: 50, Handler: sortKeysOperator}
+
 var joinStringOpType = &operationType{Type: "JOIN", NumArgs: 1, Precedence: 50, Handler: joinStringOperator}
 var subStringOpType = &operationType{Type: "SUBSTR", NumArgs: 1, Precedence: 50, Handler: substituteStringOperator}
 var matchOpType = &operationType{Type: "MATCH", NumArgs: 1, Precedence: 50, Handler: matchOperator}
 var captureOpType = &operationType{Type: "CAPTURE", NumArgs: 1, Precedence: 50, Handler: captureOperator}
 var testOpType = &operationType{Type: "TEST", NumArgs: 1, Precedence: 50, Handler: testOperator}
 var splitStringOpType = &operationType{Type: "SPLIT", NumArgs: 1, Precedence: 50, Handler: splitStringOperator}
+var changeCaseOpType = &operationType{Type: "CHANGE_CASE", NumArgs: 0, Precedence: 50, Handler: changeCaseOperator}
 
 var loadOpType = &operationType{Type: "LOAD", NumArgs: 1, Precedence: 50, Handler: loadYamlOperator}
 
diff --git a/pkg/yqlib/operator_strings.go b/pkg/yqlib/operator_strings.go
index 2ab60fd30d..394ca3e5c4 100644
--- a/pkg/yqlib/operator_strings.go
+++ b/pkg/yqlib/operator_strings.go
@@ -9,6 +9,37 @@ import (
 	"gopkg.in/yaml.v3"
 )
 
+type changeCasePrefs struct {
+	ToUpperCase bool
+}
+
+func changeCaseOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
+	results := list.New()
+	prefs := expressionNode.Operation.Preferences.(changeCasePrefs)
+
+	for el := context.MatchingNodes.Front(); el != nil; el = el.Next() {
+		candidate := el.Value.(*CandidateNode)
+
+		node := unwrapDoc(candidate.Node)
+
+		if guessTagFromCustomType(node) != "!!str" {
+			return Context{}, fmt.Errorf("cannot change case with %v, can only operate on strings. ", node.Tag)
+		}
+
+		newStringNode := &yaml.Node{Kind: yaml.ScalarNode, Tag: node.Tag, Style: node.Style}
+		if prefs.ToUpperCase {
+			newStringNode.Value = strings.ToUpper(node.Value)
+		} else {
+			newStringNode.Value = strings.ToLower(node.Value)
+		}
+		results.PushBack(candidate.CreateReplacement(newStringNode))
+
+	}
+
+	return context.ChildContext(results), nil
+
+}
+
 func getSubstituteParameters(d *dataTreeNavigator, block *ExpressionNode, context Context) (string, string, error) {
 	regEx := ""
 	replacementText := ""
diff --git a/pkg/yqlib/operator_strings_test.go b/pkg/yqlib/operator_strings_test.go
index cf65f8a6e8..04c49f7fe4 100644
--- a/pkg/yqlib/operator_strings_test.go
+++ b/pkg/yqlib/operator_strings_test.go
@@ -5,6 +5,40 @@ import (
 )
 
 var stringsOperatorScenarios = []expressionScenario{
+	{
+		description:    "To up (upper) case",
+		subdescription: "Works with unicode characters",
+		document:       `água`,
+		expression:     "upcase",
+		expected: []string{
+			"D0, P[], (!!str)::ÁGUA\n",
+		},
+	},
+	{
+		skipDoc:    true,
+		document:   `!camel água`,
+		expression: "upcase",
+		expected: []string{
+			"D0, P[], (!camel)::ÁGUA\n",
+		},
+	},
+	{
+		description:    "To down (lower) case",
+		subdescription: "Works with unicode characters",
+		document:       `ÁgUA`,
+		expression:     "downcase",
+		expected: []string{
+			"D0, P[], (!!str)::água\n",
+		},
+	},
+	{
+		skipDoc:    true,
+		document:   `!camel ÁgUA`,
+		expression: "downcase",
+		expected: []string{
+			"D0, P[], (!camel)::água\n",
+		},
+	},
 	{
 		description: "Join strings",
 		document:    `[cat, meow, 1, null, true]`,