diff --git a/bootstrap b/bootstrap
index 4564ae8ff..96b4387c5 100755
--- a/bootstrap
+++ b/bootstrap
@@ -2,14 +2,25 @@
 %% -*- mode: erlang;erlang-indent-level: 4;indent-tabs-mode: nil -*-
 %% ex: ft=erlang ts=4 sw=4 et
 
-main(_) ->
+main(Args) ->
+    case lists:member("--offline", Args) of
+        true ->
+            os:putenv("REBAR_OFFLINE", "1");
+        false ->
+            ok
+    end,
     ensure_app(crypto),
     ensure_app(asn1),
     ensure_app(public_key),
-    ensure_app(ssl),
-    inets:start(),
-    inets:start(httpc, [{profile, rebar}]),
-    set_httpc_options(),
+    case os:getenv("REBAR_OFFLINE") of
+        "1" ->
+            ok;
+        _ ->
+            ensure_app(ssl),
+            inets:start(),
+            inets:start(httpc, [{profile, rebar}]),
+            set_httpc_options()
+    end,
 
     %% Clear directories for builds since bootstrapping may require
     %% a changed structure from an older one
@@ -117,6 +128,14 @@ extract(Binary) ->
     {ok, Contents}.
 
 request(Url) ->
+    case os:getenv("REBAR_OFFLINE") of
+        "1" ->
+            {error, {offline, Url}};
+        _ ->
+            request_online(Url)
+    end.
+
+request_online(Url) ->
     HttpOptions = [{relaxed, true} | get_proxy_auth()],
 
     case httpc:request(get, {Url, []},
diff --git a/src/rebar3.erl b/src/rebar3.erl
index a0b9266f5..3e80ea0c5 100644
--- a/src/rebar3.erl
+++ b/src/rebar3.erl
@@ -177,17 +177,27 @@ run_aux(State, RawArgs) ->
     State9 = rebar_state:default(State8, rebar_state:opts(State8)),
 
     {Task, Args} = parse_args(RawArgs),
+    Offline = case lists:member("--offline", Args) of
+                  true ->
+                      %% We store this redundantly in env, because some APIs
+                      %% don't get a state.
+                      os:putenv("REBAR_OFFLINE", "1"),
+                      true;
+                  false ->
+                      os:getenv("REBAR_OFFLINE") =:= "1"
+              end,
+    State10 = rebar_state:set(State9, offline, Offline),
 
-    State10 = rebar_state:code_paths(State9, default, code:get_path()),
+    State11 = rebar_state:code_paths(State10, default, code:get_path()),
 
-    case rebar_core:init_command(rebar_state:command_args(State10, Args), Task) of
-        {ok, State11} ->
+    case rebar_core:init_command(rebar_state:command_args(State11, Args), Task) of
+        {ok, State12} ->
             case rebar_state:get(State11, caller, command_line) of
                 api ->
                     rebar_paths:unset_paths([deps, plugins], State11),
-                    {ok, State11};
+                    {ok, State12};
                 _ ->
-                    {ok, State11}
+                    {ok, State12}
             end;
         Other ->
             Other
@@ -377,9 +387,14 @@ start_and_load_apps(Caller) ->
     ensure_running(crypto, Caller),
     ensure_running(asn1, Caller),
     ensure_running(public_key, Caller),
-    ensure_running(ssl, Caller),
-    ensure_running(inets, Caller),
-    inets:start(httpc, [{profile, rebar}]).
+    case os:getenv("REBAR_OFFLINE") of
+        "1" ->
+            ok;
+        _ ->
+            ensure_running(ssl, Caller),
+            ensure_running(inets, Caller),
+            inets:start(httpc, [{profile, rebar}])
+    end.
 
 %% @doc Make sure a required app is running, or display an error message
 %% and abort if there's a problem.
diff --git a/src/rebar_fetch.erl b/src/rebar_fetch.erl
index d32a42312..28753a308 100644
--- a/src/rebar_fetch.erl
+++ b/src/rebar_fetch.erl
@@ -50,6 +50,14 @@ download_source(AppInfo, State)  ->
     end.
 
 download_source_(AppInfo, State) ->
+    case rebar_state:get(State, offline, false) of
+        true ->
+            {error, {?MODULE, offline}};
+        false ->
+            download_source_online(AppInfo, State)
+    end.
+
+download_source_online(AppInfo, State) ->
     AppDir = rebar_app_info:dir(AppInfo),
     TmpDir = ec_file:insecure_mkdtemp(),
     AppDir1 = rebar_utils:to_list(AppDir),
@@ -68,6 +76,17 @@ download_source_(AppInfo, State) ->
 -spec needs_update(rebar_app_info:t(), rebar_state:t())
                   -> boolean() | {error, string()}.
 needs_update(AppInfo, State) ->
+    case rebar_state:get(State, offline, false) of
+        true ->
+            ?DEBUG("Can't check if dependency needs updates in offline mode", []),
+            false;
+        false ->
+            needs_update_online(AppInfo, State)
+    end.
+
+-spec needs_update_online(rebar_app_info:t(), rebar_state:t())
+                         -> boolean() | {error, string()}.
+needs_update_online(AppInfo, State) ->
     try
         rebar_resource_v2:needs_update(AppInfo, State)
     catch
diff --git a/src/rebar_httpc_adapter.erl b/src/rebar_httpc_adapter.erl
index b173cf6b3..26318d1ba 100644
--- a/src/rebar_httpc_adapter.erl
+++ b/src/rebar_httpc_adapter.erl
@@ -9,6 +9,18 @@
 %%====================================================================
 
 request(Method, URI, ReqHeaders, Body, AdapterConfig) ->
+    case os:getenv("REBAR_OFFLINE") of
+        "1" ->
+            {error, {offline, URI}};
+        _ ->
+            request_online(Method, URI, ReqHeaders, Body, AdapterConfig)
+    end.
+
+%%====================================================================
+%% Internal functions
+%%====================================================================
+
+request_online(Method, URI, ReqHeaders, Body, AdapterConfig) ->
     Profile = maps:get(profile, AdapterConfig, default),
     Request = build_request(URI, ReqHeaders, Body),
     SSLOpts = [{ssl, rebar_utils:ssl_opts(URI)}],
@@ -19,10 +31,6 @@ request(Method, URI, ReqHeaders, Body, AdapterConfig) ->
         {error, Reason} -> {error, Reason}
     end.
 
-%%====================================================================
-%% Internal functions
-%%====================================================================
-
 build_request(URI, ReqHeaders, Body) ->
     build_request2(binary_to_list(URI), dump_headers(ReqHeaders), Body).
 
diff --git a/src/rebar_prv_local_upgrade.erl b/src/rebar_prv_local_upgrade.erl
index 8f0d3a453..74d198da6 100644
--- a/src/rebar_prv_local_upgrade.erl
+++ b/src/rebar_prv_local_upgrade.erl
@@ -120,6 +120,19 @@ etag(Path) ->
       ETag :: false | string(),
       Res :: 'error' | {ok, cached} | {ok, any(), string()}.
 request(Url, ETag) ->
+    case os:getenv("REBAR_OFFLINE") of
+        "1" ->
+            ?DEBUG("Rebar is in offline mode", []),
+            error;
+        _ ->
+            request_online(Url, ETag)
+    end.
+
+-spec request_online(Url, ETag) -> Res when
+      Url :: string(),
+      ETag :: false | string(),
+      Res :: 'error' | {ok, cached} | {ok, any(), string()}.
+request_online(Url, ETag) ->
     HttpOptions = [{ssl, rebar_utils:ssl_opts(Url)},
                    {relaxed, true} | rebar_utils:get_proxy_auth()],
     case httpc:request(get, {Url, [{"if-none-match", "\"" ++ ETag ++ "\""}