diff --git a/src/sonic-yang-models/setup.py b/src/sonic-yang-models/setup.py
index 41787b6f3..16f3b3e36 100644
--- a/src/sonic-yang-models/setup.py
+++ b/src/sonic-yang-models/setup.py
@@ -64,6 +64,8 @@ setup(
                          './yang-models/sonic-route-common.yang',
                          './yang-models/sonic-route-map.yang',
                          './yang-models/sonic-routing-policy-sets.yang',
+                         './yang-models/sonic-system-aaa.yang',
+                         './yang-models/sonic-system-tacacs.yang',
                          './yang-models/sonic-types.yang',
                          './yang-models/sonic-versions.yang',
                          './yang-models/sonic-vlan.yang',
diff --git a/src/sonic-yang-models/tests/files/sample_config_db.json b/src/sonic-yang-models/tests/files/sample_config_db.json
index 5d1312564..2693c5c22 100644
--- a/src/sonic-yang-models/tests/files/sample_config_db.json
+++ b/src/sonic-yang-models/tests/files/sample_config_db.json
@@ -792,6 +792,22 @@
                 "polling_interval": "0"
             }
         },
+        "AAA": {
+            "authentication": {
+                "login": "local" 
+            }
+        },
+        "TACPLUS": {
+            "global": {
+                "auth_type": "pap",
+                "timeout": "5"
+            }
+        },
+        "TACPLUS_SERVER": {
+            "192.168.1.1": {
+                "timeout": "10"
+            }
+        },
 
         "NAT_BINDINGS": {
             "bind1": {
@@ -899,4 +915,5 @@
             "Error": "This Table is for testing, This Table does not have YANG models."
         }
     }
+    
 }
diff --git a/src/sonic-yang-models/tests/yang_model_tests/tests/aaa.json b/src/sonic-yang-models/tests/yang_model_tests/tests/aaa.json
new file mode 100644
index 000000000..5316c83e7
--- /dev/null
+++ b/src/sonic-yang-models/tests/yang_model_tests/tests/aaa.json
@@ -0,0 +1,13 @@
+{
+    "AAA_TEST": {
+        "desc": "Configure an authentication type in AAA table."
+    },
+    "AAA_TEST_WRONG_TYPE": {
+        "desc": "Configure a wrong type in AAA table.",
+        "eStrKey": "InvalidValue"
+    },
+    "AAA_TEST_WRONG_FAILTHROUGH": {
+        "desc": "Configure a wrong failthrough in AAA table.",
+        "eStrKey": "InvalidValue"
+    }
+}
diff --git a/src/sonic-yang-models/tests/yang_model_tests/tests/tacacs.json b/src/sonic-yang-models/tests/yang_model_tests/tests/tacacs.json
new file mode 100644
index 000000000..5236aab59
--- /dev/null
+++ b/src/sonic-yang-models/tests/yang_model_tests/tests/tacacs.json
@@ -0,0 +1,32 @@
+{
+    "TACPLUS_TEST": {
+        "desc": "Tacplus global configuration in TACPLUS table."
+    },
+    "TACPLUS_INVALID_TIMEOUT_TEST": {
+        "desc": "Tacplus global configuration with invalid timeout value in TACPLUS table.",
+	"eStr": "TACACS timeout must be 1..60"
+    },
+    "TACPLUS_NOT_PRESENT_SRC_INTF_TEST": {
+        "desc": "Tacplus global configuration with a non existent port in TACPLUS table.",
+        "eStrKey": "InvalidValue"
+    },
+    "TACPLUS_SERVER_TEST" : {
+        "desc": "Tacplus server configuration in TACPLUS_SERVER table."
+    },
+    "TACPLUS_SERVER_INVALID_PRIORITY_TEST": {
+        "desc": "Tacplus server configuration with invalid priority value in TACPLUS_SERVER table.",
+	"eStr": "TACACS server priority must be 1..64"
+    },
+    "TACPLUS_SERVER_INVALID_TIMEOUT_TEST" : {
+        "desc": "Tacplus server configuration with invalid timeout value in TACPLUS_SERVER table.",
+        "eStr": "TACACS server timeout must be 1..60"
+    },
+    "TACPLUS_SERVER_INVALID_AUTH_TYPE_TEST" : {
+        "desc": "Tacplus server configuration with invalid auth type in TACPLUS_SERVER table.",
+        "eStrKey": "InvalidValue"
+    },
+    "TACPLUS_SERVER_INVALID_VRF_TEST" : {
+        "desc": "Tacplus server configuration with invalid VRF in TACPLUS_SERVER table.",
+        "eStr": "Invalid VRF name"
+    }
+}
diff --git a/src/sonic-yang-models/tests/yang_model_tests/tests_config/aaa.json b/src/sonic-yang-models/tests/yang_model_tests/tests_config/aaa.json
new file mode 100644
index 000000000..1b79b26ac
--- /dev/null
+++ b/src/sonic-yang-models/tests/yang_model_tests/tests_config/aaa.json
@@ -0,0 +1,35 @@
+{
+    "AAA_TEST": {
+        "sonic-system-aaa:sonic-system-aaa": {
+            "sonic-system-aaa:AAA": {
+                "AAA_LIST": [{
+                        "type": "authentication",
+                        "login": "tacacs+,local",
+                        "failthrough": "true",
+                        "debug": "true"
+                }]
+            }
+        }
+    },
+
+    "AAA_TEST_WRONG_TYPE": {
+        "sonic-system-aaa:sonic-system-aaa": {
+            "sonic-system-aaa:AAA": {
+                "AAA_LIST": [{
+                        "type": "authorization"
+                }]
+            }
+        }
+    },
+
+    "AAA_TEST_WRONG_FAILTHROUGH": {
+        "sonic-system-aaa:sonic-system-aaa": {
+            "sonic-system-aaa:AAA": {
+                "AAA_LIST": [{
+                        "type": "authentication",
+                        "failthrough": "enable"
+                }]
+            }
+        }
+    }
+}
diff --git a/src/sonic-yang-models/tests/yang_model_tests/tests_config/tacacs.json b/src/sonic-yang-models/tests/yang_model_tests/tests_config/tacacs.json
new file mode 100644
index 000000000..290813121
--- /dev/null
+++ b/src/sonic-yang-models/tests/yang_model_tests/tests_config/tacacs.json
@@ -0,0 +1,131 @@
+{
+    "TACPLUS_TEST": {
+        "sonic-port:sonic-port": {
+            "sonic-port:PORT": {
+                "PORT_LIST": [
+                {
+                    "admin_status": "up",
+                    "alias": "eth8",
+                    "description": "Ethernet8",
+                    "lanes": "65",
+                    "mtu": 9000,
+                    "name": "Ethernet0",
+                    "speed": 25000
+                }
+                ]
+            }
+        },
+
+        "sonic-system-tacacs:sonic-system-tacacs": {
+            "sonic-system-tacacs:TACPLUS": {
+                "global": {
+                        "auth_type": "chap",
+                        "timeout": 5,
+                        "passkey": "dellsonic",
+                        "src_intf": "Ethernet0"
+                }
+            }
+        }
+    },
+
+    "TACPLUS_INVALID_TIMEOUT_TEST": {
+        "sonic-system-tacacs:sonic-system-tacacs": {
+            "sonic-system-tacacs:TACPLUS": {
+                "global": {
+                        "auth_type": "chap",
+                        "timeout": 70
+                }
+            }
+        }
+    },
+
+    "TACPLUS_NOT_PRESENT_SRC_INTF_TEST": {
+        "sonic-system-tacacs:sonic-system-tacacs": {
+            "sonic-system-tacacs:TACPLUS": {
+                "global": {
+                        "auth_type": "chap",
+                        "timeout": 5,
+                        "passkey": "dellsonic",
+                        "src_intf": "Ethernet0"
+                }
+            }
+        }
+    },
+
+    "TACPLUS_SERVER_TEST": {
+        "sonic-system-tacacs:sonic-system-tacacs": {
+            "sonic-system-tacacs:TACPLUS_SERVER": {
+                "TACPLUS_SERVER_LIST": [
+                {
+                        "ipaddress": "192.168.1.1",
+                        "priority": 5,
+                        "tcp_port": 50,
+                        "timeout": 10,
+                        "auth_type": "chap",
+                        "passkey": "dellsonic",
+                        "vrf": "default"
+                },
+                {
+                        "ipaddress": "tacserver1",
+                        "priority": 2,
+                        "tcp_port": 51,
+                        "timeout": 15,
+                        "auth_type": "pap",
+                        "passkey": "dellsonic1",
+                        "vrf": "mgmt"
+                }
+                ]
+            }
+        }
+    },
+
+    "TACPLUS_SERVER_INVALID_PRIORITY_TEST": {
+        "sonic-system-tacacs:sonic-system-tacacs": {
+            "sonic-system-tacacs:TACPLUS_SERVER": {
+                "TACPLUS_SERVER_LIST": [
+                {
+                    "ipaddress": "192.168.1.1",
+                    "priority": 70
+                }
+                ]
+            }
+        }
+    },
+    "TACPLUS_SERVER_INVALID_TIMEOUT_TEST": {
+        "sonic-system-tacacs:sonic-system-tacacs": {
+            "sonic-system-tacacs:TACPLUS_SERVER": {
+                "TACPLUS_SERVER_LIST": [
+                {
+                    "ipaddress": "192.168.1.1",
+                    "timeout": 70
+                }
+                ]
+            }
+        }
+    },
+    "TACPLUS_SERVER_INVALID_AUTH_TYPE_TEST": {
+        "sonic-system-tacacs:sonic-system-tacacs": {
+            "sonic-system-tacacs:TACPLUS_SERVER": {
+                "TACPLUS_SERVER_LIST": [
+                {
+                    "ipaddress": "192.168.1.1",
+                    "auth_type": "123"
+                }
+                ]
+            }
+        }
+    },
+    "TACPLUS_SERVER_INVALID_VRF_TEST": {
+        "sonic-system-tacacs:sonic-system-tacacs": {
+            "sonic-system-tacacs:TACPLUS_SERVER": {
+                "TACPLUS_SERVER_LIST": [
+                {
+                    "ipaddress": "192.168.1.1",
+                    "vrf": "Vrf1"
+                }
+                ]
+            }
+        }
+    }
+
+}
diff --git a/src/sonic-yang-models/yang-models/sonic-system-aaa.yang b/src/sonic-yang-models/yang-models/sonic-system-aaa.yang
new file mode 100644
index 000000000..eb6a8b06c
--- /dev/null
+++ b/src/sonic-yang-models/yang-models/sonic-system-aaa.yang
@@ -0,0 +1,44 @@
+module sonic-system-aaa {
+    namespace "http://github.com/Azure/sonic-system-aaa";
+    prefix ssys;
+    yang-version 1.1;
+
+    revision 2021-04-15 {
+        description "Initial revision.";
+    }
+
+    container sonic-system-aaa {
+        container AAA {
+            list AAA_LIST {
+                key "type";
+
+                leaf type {
+                    type enumeration {
+                        enum authentication;
+                    }
+                    description "AAA type authentication";
+                }
+
+                leaf login {
+                    type string;
+                    description "AAA authentication methods - local/tacacs+";
+                    default "local";
+                }
+
+                leaf failthrough {
+                    type boolean;
+                    description "When set to true, authentication is attempted on next configured server/local in the list upon failure.";
+                    default false;
+                }
+                
+                leaf debug {
+                    type boolean;
+                    description "Enable/disable AAA debugging";
+                    default false;
+                }
+
+            }
+        }
+    }
+}
+
diff --git a/src/sonic-yang-models/yang-models/sonic-system-tacacs.yang b/src/sonic-yang-models/yang-models/sonic-system-tacacs.yang
new file mode 100644
index 000000000..f82340b0e
--- /dev/null
+++ b/src/sonic-yang-models/yang-models/sonic-system-tacacs.yang
@@ -0,0 +1,172 @@
+module sonic-system-tacacs {
+    namespace "http://github.com/Azure/sonic-system-tacacs";
+    prefix ssys;
+    yang-version 1.1;
+
+    import ietf-inet-types {
+        prefix inet;
+    }
+
+    import sonic-port {
+        prefix port;
+    }
+
+    import sonic-portchannel {
+        prefix lag;
+    }
+
+    /*
+    import sonic-vlan {
+        prefix vlan;
+    }
+    */
+
+    import sonic-loopback-interface {
+        prefix loopback;
+    }
+
+    import sonic-interface {
+        prefix interface;
+    }
+
+    import sonic-mgmt_port {
+        prefix mgmt-port;
+    }
+
+    revision 2021-04-15 {
+        description "Initial revision.";
+    }
+
+    typedef auth_type_enumeration {
+        type enumeration {
+            enum pap;
+            enum chap;
+            enum mschap;
+            enum login;
+        }
+    }
+
+    container sonic-system-tacacs {
+
+        container TACPLUS_SERVER {
+            list TACPLUS_SERVER_LIST {
+                max-elements 8;
+                key "ipaddress";
+
+                leaf ipaddress {
+                    type inet:host;
+                    description
+                        "TACACS+ server's Domain name or IP address (IPv4 or IPv6)";
+                }
+
+                leaf priority {
+                    default 1;
+                    type uint8 {
+                        range "1..64" {
+                            error-message "TACACS server priority must be 1..64";
+                        }
+                    }
+                    description "Server priority";
+                }
+
+                leaf tcp_port {
+                    type inet:port-number;
+                    default 49;
+                    description "TCP port to communite with TACACS+ server";
+                }
+
+                leaf timeout {
+                    default 5;
+                    type uint16 {
+                        range "1..60" {
+                            error-message "TACACS server timeout must be 1..60";
+                        }
+                    }
+                    description "TACACS+ server timeout";
+                }
+
+                leaf auth_type {
+                    type auth_type_enumeration;
+                    default pap;
+                    description "Authentication type";
+                }
+
+                leaf passkey {
+                    type string {
+                        length "1..65";
+                        pattern "[^ #,]*" {
+                            error-message 'TACACS shared secret (Valid chars are ASCII printable except SPACE, "#", and ",")';
+                        }
+                    }
+                }
+
+                leaf vrf {
+                    type string {
+                        pattern "mgmt|default" {
+                            error-message "Error: Invalid VRF name";
+                        }
+                    }
+                    description
+                        "VRF name";
+                }
+            }
+        }
+
+
+        container TACPLUS {
+
+            container global {
+
+                leaf auth_type {
+                    type auth_type_enumeration;
+                    default pap;
+                }
+
+                leaf timeout {
+                    type uint16 {
+                        range "1..60" {
+                            error-message "TACACS timeout must be 1..60";
+                        }
+                    }
+                    default 5;
+                }
+
+                leaf passkey {
+                    type string {
+                        length "1..65";
+                        pattern "[^ #,]*" {
+                            error-message 'TACACS shared secret (Valid chars are ASCII printable except SPACE, "#", and ",")';
+                        }
+                    }
+                    description "Shared secret used for encrypting the communication";
+                }
+
+                leaf src_intf {
+                    type union {
+                        type leafref {
+                            path "/port:sonic-port/port:PORT/port:PORT_LIST/port:name";
+                        }
+                        type leafref {
+                            path "/lag:sonic-portchannel/lag:PORTCHANNEL/lag:PORTCHANNEL_LIST/lag:name";
+                        }
+                        /*
+                        type leafref {
+                            path "/vlan:sonic-vlan/vlan:VLAN/vlan:VLAN_LIST/vlan:name";
+                        }
+                        */
+                        type string {
+                            pattern 'Vlan([0-9]{1,3}|[1-3][0-9]{3}|[4][0][0-8][0-9]|[4][0][9][0-4])';
+                        }
+                        type leafref {
+                            path "/loopback:sonic-loopback-interface/loopback:LOOPBACK_INTERFACE/loopback:LOOPBACK_INTERFACE_LIST/loopback:name";
+                        }
+                        type leafref {
+                            path "/mgmt-port:sonic-mgmt_port/mgmt-port:MGMT_PORT/mgmt-port:MGMT_PORT_LIST/mgmt-port:name";
+                        }
+                    }
+                    description "Source IP to use from source interface for TACACS+ server communication.";
+                }
+            }
+        }
+    }
+}