diff --git a/changes/21264-fix-reserved-team-names b/changes/21264-fix-reserved-team-names
new file mode 100644
index 0000000000..6363b81869
--- /dev/null
+++ b/changes/21264-fix-reserved-team-names
@@ -0,0 +1,2 @@
+- Prevents teams with the name "All teams" or "No team" from being created (these are reserved team
+  names in Fleet).
\ No newline at end of file
diff --git a/cmd/fleetctl/gitops_test.go b/cmd/fleetctl/gitops_test.go
index ba4124f4e0..63528fea2d 100644
--- a/cmd/fleetctl/gitops_test.go
+++ b/cmd/fleetctl/gitops_test.go
@@ -395,6 +395,27 @@ software:
 	require.Error(t, err)
 	assert.Contains(t, err.Error(), "'name' is required")
 
+	// reserved team name; should error in both dry run and real
+	t.Setenv("TEST_TEAM_NAME", "no TEam")
+	_, err = runAppNoChecks([]string{"gitops", "-f", tmpFile.Name(), "--dry-run"})
+	require.Error(t, err)
+	assert.Contains(t, err.Error(), `"No team" is a reserved team name`)
+
+	t.Setenv("TEST_TEAM_NAME", "no TEam")
+	_, err = runAppNoChecks([]string{"gitops", "-f", tmpFile.Name()})
+	require.Error(t, err)
+	assert.Contains(t, err.Error(), `"No team" is a reserved team name`)
+
+	t.Setenv("TEST_TEAM_NAME", "All teams")
+	_, err = runAppNoChecks([]string{"gitops", "-f", tmpFile.Name(), "--dry-run"})
+	require.Error(t, err)
+	assert.Contains(t, err.Error(), `"All teams" is a reserved team name`)
+
+	t.Setenv("TEST_TEAM_NAME", "All TEAMS")
+	_, err = runAppNoChecks([]string{"gitops", "-f", tmpFile.Name()})
+	require.Error(t, err)
+	assert.Contains(t, err.Error(), `"All teams" is a reserved team name`)
+
 	// Dry run
 	t.Setenv("TEST_TEAM_NAME", teamName)
 	_ = runAppForTest(t, []string{"gitops", "-f", tmpFile.Name(), "--dry-run"})
diff --git a/ee/server/service/teams.go b/ee/server/service/teams.go
index bb8e01342b..448abc3674 100644
--- a/ee/server/service/teams.go
+++ b/ee/server/service/teams.go
@@ -7,6 +7,7 @@ import (
 	"fmt"
 	"net/http"
 	"net/url"
+	"strings"
 
 	"github.com/fleetdm/fleet/v4/pkg/optjson"
 	"github.com/fleetdm/fleet/v4/server"
@@ -73,6 +74,13 @@ func (svc *Service) NewTeam(ctx context.Context, p fleet.TeamPayload) (*fleet.Te
 	if *p.Name == "" {
 		return nil, fleet.NewInvalidArgumentError("name", "may not be empty")
 	}
+	l := strings.ToLower(*p.Name)
+	if l == strings.ToLower(fleet.ReservedNameAllTeams) {
+		return nil, fleet.NewInvalidArgumentError("name", `"All teams" is a reserved team name`)
+	}
+	if l == strings.ToLower(fleet.ReservedNameNoTeam) {
+		return nil, fleet.NewInvalidArgumentError("name", `"No team" is a reserved team name`)
+	}
 	team.Name = *p.Name
 
 	if p.Description != nil {
@@ -129,6 +137,13 @@ func (svc *Service) ModifyTeam(ctx context.Context, teamID uint, payload fleet.T
 		if *payload.Name == "" {
 			return nil, fleet.NewInvalidArgumentError("name", "may not be empty")
 		}
+		l := strings.ToLower(*payload.Name)
+		if l == strings.ToLower(fleet.ReservedNameAllTeams) {
+			return nil, fleet.NewInvalidArgumentError("name", `"All teams" is a reserved team name`)
+		}
+		if l == strings.ToLower(fleet.ReservedNameNoTeam) {
+			return nil, fleet.NewInvalidArgumentError("name", `"No team" is a reserved team name`)
+		}
 		team.Name = *payload.Name
 	}
 	if payload.Description != nil {
@@ -860,6 +875,14 @@ func (svc *Service) ApplyTeamSpecs(ctx context.Context, specs []*fleet.TeamSpec,
 			}
 		}
 
+		l := strings.ToLower(spec.Name)
+		if l == strings.ToLower(fleet.ReservedNameAllTeams) {
+			return nil, fleet.NewInvalidArgumentError("name", `"All teams" is a reserved team name`)
+		}
+		if l == strings.ToLower(fleet.ReservedNameNoTeam) {
+			return nil, fleet.NewInvalidArgumentError("name", `"No team" is a reserved team name`)
+		}
+
 		var team *fleet.Team
 		// If filename is provided, try to find the team by filename first.
 		// This is needed in case user is trying to modify the team name.
@@ -883,6 +906,7 @@ func (svc *Service) ApplyTeamSpecs(ctx context.Context, specs []*fleet.TeamSpec,
 				}
 			}
 		}
+
 		var create bool
 		if team == nil {
 			team, err = svc.ds.TeamByName(ctx, spec.Name)
diff --git a/frontend/pages/admin/TeamManagementPage/TeamDetailsWrapper/TeamDetailsWrapper.tsx b/frontend/pages/admin/TeamManagementPage/TeamDetailsWrapper/TeamDetailsWrapper.tsx
index 90a3d609d9..dc7d191ec2 100644
--- a/frontend/pages/admin/TeamManagementPage/TeamDetailsWrapper/TeamDetailsWrapper.tsx
+++ b/frontend/pages/admin/TeamManagementPage/TeamDetailsWrapper/TeamDetailsWrapper.tsx
@@ -337,11 +337,18 @@ const TeamDetailsWrapper = ({
           setBackendValidators({
             name: "A team with this name already exists",
           });
+        } else if (errorObject.base.includes("all teams")) {
+          setBackendValidators({
+            name: `"All teams" is a reserved team name. Please try another name.`,
+          });
+        } else if (errorObject.base.includes("no team")) {
+          setBackendValidators({
+            name: `"No team" is a reserved team name. Please try another name.`,
+          });
         } else {
           renderFlash("error", "Could not create team. Please try again.");
         }
       } finally {
-        toggleRenameTeamModal();
         setIsUpdatingTeams(false);
       }
     },
diff --git a/frontend/pages/admin/TeamManagementPage/TeamManagementPage.tsx b/frontend/pages/admin/TeamManagementPage/TeamManagementPage.tsx
index 92bbec0280..7243f01eed 100644
--- a/frontend/pages/admin/TeamManagementPage/TeamManagementPage.tsx
+++ b/frontend/pages/admin/TeamManagementPage/TeamManagementPage.tsx
@@ -116,6 +116,14 @@ const TeamManagementPage = (): JSX.Element => {
             setBackendValidators({
               name: "A team with this name already exists",
             });
+          } else if (createError.data.errors[0].reason.includes("all teams")) {
+            setBackendValidators({
+              name: `"All teams" is a reserved team name. Please try another name.`,
+            });
+          } else if (createError.data.errors[0].reason.includes("no team")) {
+            setBackendValidators({
+              name: `"No team" is a reserved team name. Please try another name.`,
+            });
           } else {
             renderFlash("error", "Could not create team. Please try again.");
             toggleCreateTeamModal();
@@ -185,6 +193,16 @@ const TeamManagementPage = (): JSX.Element => {
               setBackendValidators({
                 name: "A team with this name already exists",
               });
+            } else if (
+              updateError.data.errors[0].reason.includes("all teams")
+            ) {
+              setBackendValidators({
+                name: `"All teams" is a reserved team name.`,
+              });
+            } else if (updateError.data.errors[0].reason.includes("no team")) {
+              setBackendValidators({
+                name: `"No team" is a reserved team name. Please try another name.`,
+              });
             } else {
               renderFlash(
                 "error",
diff --git a/server/service/integration_enterprise_test.go b/server/service/integration_enterprise_test.go
index b4f4148bb3..838a06936f 100644
--- a/server/service/integration_enterprise_test.go
+++ b/server/service/integration_enterprise_test.go
@@ -1120,6 +1120,20 @@ func (s *integrationEnterpriseTestSuite) TestTeamEndpoints() {
 	tmResp.Team = nil
 	s.DoJSON("POST", "/api/latest/fleet/teams", team2, http.StatusConflict, &tmResp)
 
+	// create a team with reserved team names; should be case-insensitive
+	teamReserved := &fleet.Team{
+		Name:        "no TeAm",
+		Description: "description",
+		Secrets:     []*fleet.EnrollSecret{{Secret: "foobar"}},
+	}
+
+	r := s.Do("POST", "/api/latest/fleet/teams", teamReserved, http.StatusUnprocessableEntity)
+	require.Contains(t, extractServerErrorText(r.Body), `"No team" is a reserved team name`)
+
+	teamReserved.Name = "AlL TeaMS"
+	r = s.Do("POST", "/api/latest/fleet/teams", teamReserved, http.StatusUnprocessableEntity)
+	require.Contains(t, extractServerErrorText(r.Body), `"All teams" is a reserved team name`)
+
 	// create a team with too many secrets
 	team3 := &fleet.Team{
 		Name:        name + "lots_of_secrets",
@@ -1219,6 +1233,13 @@ func (s *integrationEnterpriseTestSuite) TestTeamEndpoints() {
 	modifyExpiry.HostExpirySettings.HostExpiryWindow = 0
 	s.DoJSON("PATCH", fmt.Sprintf("/api/latest/fleet/teams/%d", tm1ID), modifyExpiry, http.StatusUnprocessableEntity, &tmResp)
 
+	// try to rename to reserved names
+	r = s.Do("PATCH", fmt.Sprintf("/api/latest/fleet/teams/%d", tm1ID), fleet.TeamPayload{Name: ptr.String("no TEAM")}, http.StatusUnprocessableEntity)
+	require.Contains(t, extractServerErrorText(r.Body), `"No team" is a reserved team name`)
+
+	r = s.Do("PATCH", fmt.Sprintf("/api/latest/fleet/teams/%d", tm1ID), fleet.TeamPayload{Name: ptr.String("ALL teAMs")}, http.StatusUnprocessableEntity)
+	require.Contains(t, extractServerErrorText(r.Body), `"All teams" is a reserved team name`)
+
 	// Modify team's calendar config
 	modifyCalendar := fleet.TeamPayload{
 		Integrations: &fleet.TeamIntegrations{
diff --git a/server/service/teams.go b/server/service/teams.go
index 1d8a30032d..d2bcf6a994 100644
--- a/server/service/teams.go
+++ b/server/service/teams.go
@@ -5,11 +5,12 @@ import (
 	"crypto/x509"
 	"encoding/json"
 	"fmt"
-	"golang.org/x/text/unicode/norm"
 	"io"
 	"net/http"
 	"net/url"
 
+	"golang.org/x/text/unicode/norm"
+
 	"github.com/fleetdm/fleet/v4/server/contexts/ctxerr"
 	"github.com/fleetdm/fleet/v4/server/fleet"
 )