EAP-TLS and PEAP both provide secure authentication methods, but they differ in their requirements for client-side authentication. EAP-TLS requires both the client (supplicant) and the server to authenticate each other with certificates, thereby ensuring a very high level of security. On the other hand, PEAP requires a server-side certificate to create a secure tunnel and allows the client to authenticate using less stringent methods, such as a username and password, which are then protected by the tunnel. This makes PEAP more flexible in environments where client-side certificates are not feasible.