diff --git a/v3/process_instances.go b/v3/process_instances.go
new file mode 100644
index 000000000..591b3fd85
--- /dev/null
+++ b/v3/process_instances.go
@@ -0,0 +1,143 @@
+package v3
+
+import (
+	"encoding/json"
+	"fmt"
+	"time"
+
+	. "github.com/cloudfoundry/cf-acceptance-tests/cats_suite_helpers"
+	"github.com/cloudfoundry/cf-acceptance-tests/helpers/app_helpers"
+	"github.com/cloudfoundry/cf-acceptance-tests/helpers/assets"
+	"github.com/cloudfoundry/cf-acceptance-tests/helpers/random_name"
+	"github.com/cloudfoundry/cf-acceptance-tests/helpers/v3_helpers"
+	"github.com/cloudfoundry/cf-test-helpers/v2/cf"
+	. "github.com/onsi/ginkgo/v2"
+	. "github.com/onsi/gomega"
+	. "github.com/onsi/gomega/gbytes"
+	. "github.com/onsi/gomega/gexec"
+)
+
+type ProcessInstance struct {
+	Index int    `json:"index"`
+	State string `json:"state"`
+	Since int    `json:"since"`
+}
+
+type ProcessInstancesResource struct {
+	ProcessInstances []ProcessInstance `json:"resources"`
+}
+
+type ProcessResource struct {
+	ProcessInstances []ProcessInstance `json:"process_instances"`
+}
+
+type ProcessesResource struct {
+	Processes []ProcessResource `json:"resources"`
+}
+
+var _ = V3Describe("process instances", func() {
+	var (
+		appName    string
+		webProcess v3_helpers.Process
+	)
+
+	BeforeEach(func() {
+		appName = random_name.CATSRandomName("APP")
+
+		By("pushing the app with three instances")
+		Expect(cf.Cf("push", appName, "-i", "3", "-b", Config.GetRubyBuildpackName(), "-p", assets.NewAssets().DoraZip).Wait(Config.CfPushTimeoutDuration())).To(Exit(0))
+
+		By("waiting until all instances are running")
+		Eventually(func(g Gomega) {
+			session := cf.Cf("app", appName).Wait()
+			g.Expect(session).Should(Say(`instances:\s+3/3`))
+		}).Should(Succeed())
+
+		appGuid := app_helpers.GetAppGuid(appName)
+		processes := v3_helpers.GetProcesses(appGuid, appName)
+		webProcess = v3_helpers.GetProcessByType(processes, "web")
+	})
+
+	AfterEach(func() {
+		app_helpers.AppReport(appName)
+		Expect(cf.Cf("delete", appName, "-f").Wait(Config.DefaultTimeoutDuration())).To(Exit(0))
+	})
+
+	Context("via different v3 API endpoints", func() {
+		It("returns an array of process instances", func() {
+			By("/v3/processes/:guid/process_instances")
+			{
+				resource := ProcessInstancesResource{}
+				getResource(fmt.Sprintf("v3/processes/%s/process_instances", webProcess.Guid), &resource)
+				Expect(len(resource.ProcessInstances)).To(Equal(3))
+
+				for index, instance := range resource.ProcessInstances {
+					checkProcessInstance(instance, index, "RUNNING")
+				}
+			}
+
+			By("/v3/processes/:guid?embed=process_instances")
+			{
+				resource := ProcessResource{}
+				getResource(fmt.Sprintf("v3/processes/%s?embed=process_instances", webProcess.Guid), &resource)
+				Expect(len(resource.ProcessInstances)).To(Equal(3))
+
+				for index, instance := range resource.ProcessInstances {
+					checkProcessInstance(instance, index, "RUNNING")
+				}
+			}
+
+			By("/v3/processes?guids=:guid&embed=process_instances")
+			{
+				resource := ProcessesResource{}
+				getResource(fmt.Sprintf("v3/processes?guids=%s&embed=process_instances", webProcess.Guid), &resource)
+				Expect(len(resource.Processes)).To(Equal(1))
+				Expect(len(resource.Processes[0].ProcessInstances)).To(Equal(3))
+
+				for index, instance := range resource.Processes[0].ProcessInstances {
+					checkProcessInstance(instance, index, "RUNNING")
+				}
+			}
+		})
+	})
+
+	Context("when stopping the app", func() {
+		It("switches the instances' state from RUNNING to DOWN", func() {
+			resource := ProcessInstancesResource{}
+			getResource(fmt.Sprintf("v3/processes/%s/process_instances", webProcess.Guid), &resource)
+			Expect(len(resource.ProcessInstances)).To(Equal(3))
+
+			for index, instance := range resource.ProcessInstances {
+				checkProcessInstance(instance, index, "RUNNING")
+			}
+
+			By("stopping the app")
+			Expect(cf.Cf("stop", appName).Wait(Config.DefaultTimeoutDuration())).To(Exit(0))
+
+			By("waiting until all instances are stopped")
+			Eventually(func() []string {
+				getResource(fmt.Sprintf("v3/processes/%s/process_instances", webProcess.Guid), &resource)
+				states := []string{}
+				for _, instance := range resource.ProcessInstances {
+					states = append(states, instance.State)
+				}
+				return states
+			}, V3_PROCESS_TIMEOUT, 1*time.Second).Should(Equal([]string{"DOWN", "DOWN", "DOWN"}))
+			Expect(len(resource.ProcessInstances)).To(Equal(3))
+
+			for index, instance := range resource.ProcessInstances {
+				checkProcessInstance(instance, index, "DOWN")
+			}
+		})
+	})
+})
+
+func getResource(url string, resource any) {
+	json.Unmarshal(cf.Cf("curl", url).Wait().Out.Contents(), &resource)
+}
+
+func checkProcessInstance(instance ProcessInstance, index int, state string) {
+	Expect(instance.Index).To(Equal(index))
+	Expect(instance.State).To(Equal(state))
+	Expect(instance.Since).To(BeNumerically(">", 0))
+}