diff --git a/.changes/unreleased/NOTES-20230906-055849.yaml b/.changes/unreleased/NOTES-20230906-055849.yaml
new file mode 100644
index 000000000..a6d9ef9b3
--- /dev/null
+++ b/.changes/unreleased/NOTES-20230906-055849.yaml
@@ -0,0 +1,8 @@
+kind: NOTES
+body: 'all: This Go module has been updated to Go 1.20 per the [Go support
+  policy](https://go.dev/doc/devel/release#policy). It is recommended to review
+  the [Go 1.20 release notes](https://go.dev/doc/go1.20) before upgrading. Any
+  consumers building on earlier Go versions may experience errors.'
+time: 2023-09-06T05:58:49.879435-04:00
+custom:
+  Issue: "180"
diff --git a/.github/workflows/ci-go.yml b/.github/workflows/ci-go.yml
index 34d9b91e3..a703e9cb4 100644
--- a/.github/workflows/ci-go.yml
+++ b/.github/workflows/ci-go.yml
@@ -27,7 +27,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        go-version: [ '1.20', '1.19' ]
+        go-version: [ '1.21', '1.20' ]
     steps:
       - uses: actions/checkout@c85c95e3d7251135ab7dc9ce3241c5835cc595a9 # v3.5.3
       - uses: actions/setup-go@93397bea11091df50f3d7e59dc26a7711a8bcfbe # v4.1.0
diff --git a/README.md b/README.md
index 8342917c3..e03f8de35 100644
--- a/README.md
+++ b/README.md
@@ -9,7 +9,7 @@ When run from the root of a Terraform Provider codebase, Terraform’s testing f
 
 This project follows the [support policy](https://golang.org/doc/devel/release.html#policy) of Go as its support policy. The two latest major releases of Go are supported by the project.
 
-Currently, that means Go **1.19** or later must be used when including this project as a dependency.
+Currently, that means Go **1.20** or later must be used when including this project as a dependency.
 
 ## Contributing
 
diff --git a/go.mod b/go.mod
index 590513733..c4b803ec7 100644
--- a/go.mod
+++ b/go.mod
@@ -1,12 +1,11 @@
 module github.com/hashicorp/terraform-plugin-testing
 
-go 1.19
+go 1.20
 
 require (
 	github.com/google/go-cmp v0.5.9
 	github.com/hashicorp/go-cty v1.4.1-0.20200414143053-d3edf31b6320
 	github.com/hashicorp/go-hclog v1.5.0
-	github.com/hashicorp/go-multierror v1.1.1
 	github.com/hashicorp/go-uuid v1.0.3
 	github.com/hashicorp/go-version v1.6.0
 	github.com/hashicorp/hc-install v0.6.0
@@ -35,6 +34,7 @@ require (
 	github.com/hashicorp/errwrap v1.0.0 // indirect
 	github.com/hashicorp/go-checkpoint v0.5.0 // indirect
 	github.com/hashicorp/go-cleanhttp v0.5.2 // indirect
+	github.com/hashicorp/go-multierror v1.1.1 // indirect
 	github.com/hashicorp/go-plugin v1.4.10 // indirect
 	github.com/hashicorp/terraform-registry-address v0.2.1 // indirect
 	github.com/hashicorp/terraform-svchost v0.1.1 // indirect
diff --git a/helper/acctest/random.go b/helper/acctest/random.go
index abb778aa0..c26303eb6 100644
--- a/helper/acctest/random.go
+++ b/helper/acctest/random.go
@@ -20,10 +20,6 @@ import (
 	"golang.org/x/crypto/ssh"
 )
 
-func init() {
-	rand.Seed(time.Now().UTC().UnixNano())
-}
-
 // Helpers for generating random tidbits for use in identifiers to prevent
 // collisions in acceptance tests.
 
diff --git a/helper/resource/plan_checks.go b/helper/resource/plan_checks.go
index 712e3dbdf..c64c02ba8 100644
--- a/helper/resource/plan_checks.go
+++ b/helper/resource/plan_checks.go
@@ -5,9 +5,9 @@ package resource
 
 import (
 	"context"
+	"errors"
 
 	tfjson "github.com/hashicorp/terraform-json"
-	"github.com/hashicorp/terraform-plugin-testing/internal/errorshim"
 	"github.com/hashicorp/terraform-plugin-testing/plancheck"
 	"github.com/mitchellh/go-testing-interface"
 )
@@ -15,18 +15,14 @@ import (
 func runPlanChecks(ctx context.Context, t testing.T, plan *tfjson.Plan, planChecks []plancheck.PlanCheck) error {
 	t.Helper()
 
-	var result error
+	var result []error
 
 	for _, planCheck := range planChecks {
 		resp := plancheck.CheckPlanResponse{}
 		planCheck.CheckPlan(ctx, plancheck.CheckPlanRequest{Plan: plan}, &resp)
 
-		if resp.Error != nil {
-			// TODO: Once Go 1.20 is the minimum supported version for this module, replace with `errors.Join` function
-			// - https://github.com/hashicorp/terraform-plugin-testing/issues/99
-			result = errorshim.Join(result, resp.Error)
-		}
+		result = append(result, resp.Error)
 	}
 
-	return result
+	return errors.Join(result...)
 }
diff --git a/helper/resource/testing.go b/helper/resource/testing.go
index 2c40fc396..de96ec7a2 100644
--- a/helper/resource/testing.go
+++ b/helper/resource/testing.go
@@ -15,7 +15,6 @@ import (
 	"strings"
 	"time"
 
-	"github.com/hashicorp/go-multierror"
 	"github.com/mitchellh/go-testing-interface"
 
 	"github.com/hashicorp/terraform-plugin-go/tfprotov5"
@@ -947,7 +946,7 @@ func ComposeTestCheckFunc(fs ...TestCheckFunc) TestCheckFunc {
 	return func(s *terraform.State) error {
 		for i, f := range fs {
 			if err := f(s); err != nil {
-				return fmt.Errorf("Check %d/%d error: %s", i+1, len(fs), err)
+				return fmt.Errorf("Check %d/%d error: %w", i+1, len(fs), err)
 			}
 		}
 
@@ -965,15 +964,15 @@ func ComposeTestCheckFunc(fs ...TestCheckFunc) TestCheckFunc {
 // TestCheckFuncs and aggregates failures.
 func ComposeAggregateTestCheckFunc(fs ...TestCheckFunc) TestCheckFunc {
 	return func(s *terraform.State) error {
-		var result *multierror.Error
+		var result []error
 
 		for i, f := range fs {
 			if err := f(s); err != nil {
-				result = multierror.Append(result, fmt.Errorf("Check %d/%d error: %s", i+1, len(fs), err))
+				result = append(result, fmt.Errorf("Check %d/%d error: %w", i+1, len(fs), err))
 			}
 		}
 
-		return result.ErrorOrNil()
+		return errors.Join(result...)
 	}
 }
 
diff --git a/helper/resource/testing_test.go b/helper/resource/testing_test.go
index 811bd34e9..e3a401cd1 100644
--- a/helper/resource/testing_test.go
+++ b/helper/resource/testing_test.go
@@ -13,7 +13,6 @@ import (
 	"strings"
 	"testing"
 
-	"github.com/hashicorp/go-multierror"
 	testinginterface "github.com/mitchellh/go-testing-interface"
 
 	"github.com/hashicorp/terraform-plugin-sdk/v2/helper/schema"
@@ -54,29 +53,27 @@ func TestParallelTest(t *testing.T) {
 func TestComposeAggregateTestCheckFunc(t *testing.T) {
 	t.Parallel()
 
+	err1 := errors.New("Error 1")
 	check1 := func(s *terraform.State) error {
-		return errors.New("Error 1")
+		return err1
 	}
 
+	err2 := errors.New("Error 2")
 	check2 := func(s *terraform.State) error {
-		return errors.New("Error 2")
+		return err2
 	}
 
 	f := ComposeAggregateTestCheckFunc(check1, check2)
 	err := f(nil)
 	if err == nil {
-		t.Fatalf("Expected errors")
+		t.Fatal("expected error, got none")
 	}
 
-	multi, ok := err.(*multierror.Error)
-	if !ok {
-		t.Fatalf("unexpected type %T for err", err)
+	if !errors.Is(err, err1) {
+		t.Errorf("expected %s, got: %s", err1, err)
 	}
-	if !strings.Contains(multi.Errors[0].Error(), "Error 1") {
-		t.Fatalf("Expected Error 1, Got %s", multi.Errors[0])
-	}
-	if !strings.Contains(multi.Errors[1].Error(), "Error 2") {
-		t.Fatalf("Expected Error 2, Got %s", multi.Errors[1])
+	if !errors.Is(err, err2) {
+		t.Errorf("expected %s, got: %s", err2, err)
 	}
 }
 
diff --git a/internal/errorshim/error_join_shim.go b/internal/errorshim/error_join_shim.go
deleted file mode 100644
index b7371af82..000000000
--- a/internal/errorshim/error_join_shim.go
+++ /dev/null
@@ -1,47 +0,0 @@
-// Copyright (c) HashiCorp, Inc.
-// SPDX-License-Identifier: MPL-2.0
-
-// TODO: Once Go 1.20 is the minimum supported version delete this package, replace all usages with `errors` package
-// - https://github.com/hashicorp/terraform-plugin-testing/issues/99
-package errorshim
-
-// Copied from -> https://cs.opensource.google/go/go/+/refs/tags/go1.20.2:src/errors/join.go
-func Join(errs ...error) error {
-	n := 0
-	for _, err := range errs {
-		if err != nil {
-			n++
-		}
-	}
-	if n == 0 {
-		return nil
-	}
-	e := &joinError{
-		errs: make([]error, 0, n),
-	}
-	for _, err := range errs {
-		if err != nil {
-			e.errs = append(e.errs, err)
-		}
-	}
-	return e
-}
-
-type joinError struct {
-	errs []error
-}
-
-func (e *joinError) Error() string {
-	var b []byte
-	for i, err := range e.errs {
-		if i > 0 {
-			b = append(b, '\n')
-		}
-		b = append(b, err.Error()...)
-	}
-	return string(b)
-}
-
-func (e *joinError) Unwrap() []error {
-	return e.errs
-}
diff --git a/plancheck/expect_empty_plan.go b/plancheck/expect_empty_plan.go
index 92d55f465..14b65a248 100644
--- a/plancheck/expect_empty_plan.go
+++ b/plancheck/expect_empty_plan.go
@@ -5,9 +5,8 @@ package plancheck
 
 import (
 	"context"
+	"errors"
 	"fmt"
-
-	"github.com/hashicorp/terraform-plugin-testing/internal/errorshim"
 )
 
 var _ PlanCheck = expectEmptyPlan{}
@@ -16,17 +15,15 @@ type expectEmptyPlan struct{}
 
 // CheckPlan implements the plan check logic.
 func (e expectEmptyPlan) CheckPlan(ctx context.Context, req CheckPlanRequest, resp *CheckPlanResponse) {
-	var result error
+	var result []error
 
 	for _, rc := range req.Plan.ResourceChanges {
 		if !rc.Change.Actions.NoOp() {
-			// TODO: Once Go 1.20 is the minimum supported version for this module, replace with `errors.Join` function
-			// - https://github.com/hashicorp/terraform-plugin-testing/issues/99
-			result = errorshim.Join(result, fmt.Errorf("expected empty plan, but %s has planned action(s): %v", rc.Address, rc.Change.Actions))
+			result = append(result, fmt.Errorf("expected empty plan, but %s has planned action(s): %v", rc.Address, rc.Change.Actions))
 		}
 	}
 
-	resp.Error = result
+	resp.Error = errors.Join(result...)
 }
 
 // ExpectEmptyPlan returns a plan check that asserts that there are no resource changes in the plan.
diff --git a/terraform/state.go b/terraform/state.go
index 1e0fcb285..9cd259e0c 100644
--- a/terraform/state.go
+++ b/terraform/state.go
@@ -7,6 +7,7 @@ import (
 	"bufio"
 	"bytes"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"log"
 	"os"
@@ -17,7 +18,6 @@ import (
 	"sync"
 
 	"github.com/hashicorp/go-cty/cty"
-	"github.com/hashicorp/go-multierror"
 	"github.com/hashicorp/go-uuid"
 	"github.com/mitchellh/copystructure"
 
@@ -338,7 +338,7 @@ func (s *State) Validate() error {
 	s.Lock()
 	defer s.Unlock()
 
-	var result error
+	var result []error
 
 	// !!!! FOR DEVELOPERS !!!!
 	//
@@ -360,7 +360,7 @@ func (s *State) Validate() error {
 
 			key := strings.Join(ms.Path, ".")
 			if _, ok := found[key]; ok {
-				result = multierror.Append(result, fmt.Errorf(
+				result = append(result, fmt.Errorf(
 					strings.TrimSpace(stateValidateErrMultiModule), key))
 				continue
 			}
@@ -369,7 +369,7 @@ func (s *State) Validate() error {
 		}
 	}
 
-	return result
+	return errors.Join(result...)
 }
 
 // Remove removes the item in the state at the given address, returning
diff --git a/tfversion/any.go b/tfversion/any.go
index 27088e1a5..2fee9cb10 100644
--- a/tfversion/any.go
+++ b/tfversion/any.go
@@ -5,9 +5,8 @@ package tfversion
 
 import (
 	"context"
+	"errors"
 	"strings"
-
-	"github.com/hashicorp/terraform-plugin-testing/internal/errorshim"
 )
 
 // Any will return a nil error and empty skip message (run the test)
@@ -28,7 +27,7 @@ type anyCheck struct {
 
 // CheckTerraformVersion satisfies the TerraformVersionCheck interface.
 func (a anyCheck) CheckTerraformVersion(ctx context.Context, req CheckTerraformVersionRequest, resp *CheckTerraformVersionResponse) {
-	var joinedErrors error
+	var joinedErrors []error
 	strBuilder := strings.Builder{}
 
 	for _, subCheck := range a.terraformVersionChecks {
@@ -42,11 +41,7 @@ func (a anyCheck) CheckTerraformVersion(ctx context.Context, req CheckTerraformV
 			return
 		}
 
-		if checkResp.Error != nil {
-			// TODO: Once Go 1.20 is the minimum supported version for this module, replace with `errors.Join` function
-			// - https://github.com/hashicorp/terraform-plugin-testing/issues/99
-			joinedErrors = errorshim.Join(joinedErrors, checkResp.Error)
-		}
+		joinedErrors = append(joinedErrors, checkResp.Error)
 
 		if checkResp.Skip != "" {
 			strBuilder.WriteString(checkResp.Skip)
@@ -54,6 +49,6 @@ func (a anyCheck) CheckTerraformVersion(ctx context.Context, req CheckTerraformV
 		}
 	}
 
-	resp.Error = joinedErrors
+	resp.Error = errors.Join(joinedErrors...)
 	resp.Skip = strings.TrimSpace(strBuilder.String())
 }
diff --git a/tools/go.mod b/tools/go.mod
index fcd3f7270..c1aaab58c 100644
--- a/tools/go.mod
+++ b/tools/go.mod
@@ -1,6 +1,6 @@
 module tools
 
-go 1.19
+go 1.20
 
 require github.com/hashicorp/copywrite v0.16.4