Microservices deliver scale and agility but add discovery, traffic, security, and observability challenges. Service meshes like Istio and Linkerd add a proxy layer to automate routing, load balancing, retries, mTLS, and telemetry, freeing teams to code. Istio is rich and K8s-native but heavier; Linkerd is ultra-light and simpler. An e-commerce case shows gains in scale, reliability, and ops. Choose based on features, complexity, and resource trade-offs.