diff --git a/lib/savon/builder.rb b/lib/savon/builder.rb
index 41e9e905..ffe6f6e1 100644
--- a/lib/savon/builder.rb
+++ b/lib/savon/builder.rb
@@ -4,6 +4,7 @@
 require "savon/header"
 require "savon/message"
 require "savon/effective_options"
+require "savon/mtom"
 require "nokogiri"
 require "builder"
 require "gyoku"
@@ -18,6 +19,8 @@ module Savon
   # serialization is delegated to {Savon::Message}, the Header element to
   # {Savon::Header}, and Hash-to-XML conversion to Gyoku.
   class Builder
+    include Mtom
+
     attr_reader :multipart
 
     SCHEMA_TYPES = {
@@ -277,15 +280,17 @@ def build_multipart_message(message_xml)
 
       # the mail.body.encoded algorithm reorders the parts, default order is [ "text/plain", "text/enriched", "text/html" ]
       # should redefine the sort order, because the soap request xml should be the first
-      multipart_message.body.set_sort_order ["text/xml"]
+      multipart_message.body.set_sort_order ['application/xop+xml', 'text/xml']
 
       multipart_message.body.encoded(multipart_message.content_transfer_encoding)
     end
 
     def init_multipart_message(message_xml)
       multipart_message = Mail.new
+      apply_mtom_encoding(multipart_message, message_xml) if @locals[:mtom]
+      type = xml_part_content_type
       xml_part = Mail::Part.new do
-        content_type 'text/xml'
+        content_type type
         body message_xml
         # in Content-Type the start parameter is recommended (RFC 2387)
         content_id '<soap-request-body@soap>'
diff --git a/lib/savon/mtom.rb b/lib/savon/mtom.rb
new file mode 100644
index 00000000..a918e47c
--- /dev/null
+++ b/lib/savon/mtom.rb
@@ -0,0 +1,19 @@
+# frozen_string_literal: true
+
+module Savon
+  # MTOM request encoding (https://www.w3.org/TR/soap12-mtom/) for {Savon::Builder}.
+  module Mtom
+    private
+
+    def apply_mtom_encoding(multipart_message, message_xml)
+      multipart_message.transport_encoding = 'binary'
+      message_xml.force_encoding('BINARY')
+    end
+
+    def xml_part_content_type
+      return 'text/xml' unless @locals[:mtom]
+
+      "application/xop+xml; charset=#{@globals[:encoding]}; type=\"text/xml\""
+    end
+  end
+end
diff --git a/lib/savon/operation.rb b/lib/savon/operation.rb
index 6cd92c05..3cfc9ad0 100644
--- a/lib/savon/operation.rb
+++ b/lib/savon/operation.rb
@@ -133,14 +133,22 @@ def soap_headers(builder)
 
       if builder.multipart
         # RFC 2387 §3 (multipart/related) - SOAP envelope is the root body part
-        headers["Content-Type"] = [
-          "multipart/related",
-          "type=\"#{SOAP_REQUEST_TYPE[@globals[:soap_version]]}\"",
-          "start=\"#{builder.multipart[:start]}\"",
-          "boundary=\"#{builder.multipart[:multipart_boundary]}\""
-        ].join("; ")
+        content_type = ["multipart/related"]
+
+        if @locals[:mtom]
+          # SOAP 1.2 MTOM §3.1 - the root part is an XOP package
+          content_type << "type=\"application/xop+xml\""
+          content_type << "start-info=\"application/soap+xml\""
+        else
+          content_type << "type=\"#{SOAP_REQUEST_TYPE[@globals[:soap_version]]}\""
+        end
+
+        content_type << "start=\"#{builder.multipart[:start]}\""
+        content_type << "boundary=\"#{builder.multipart[:multipart_boundary]}\""
+
+        headers["Content-Type"] = content_type.join("; ")
         headers["MIME-Version"] = "1.0"
-        headers["Accept-Encoding"] = "gzip,deflate"
+        headers["Accept-Encoding"] = "gzip,deflate" unless @locals[:mtom]
       else
         headers["Content-Type"] = CONTENT_TYPE[@globals[:soap_version]] % @globals[:encoding]
       end
diff --git a/lib/savon/options.rb b/lib/savon/options.rb
index 8c8e854b..7f54a0cf 100644
--- a/lib/savon/options.rb
+++ b/lib/savon/options.rb
@@ -499,7 +499,8 @@ def initialize(options = {})
       defaults = {
         advanced_typecasting: true,
         response_parser: :nokogiri,
-        multipart: false
+        multipart: false,
+        mtom: false
       }
 
       super defaults.merge(options)
@@ -562,6 +563,11 @@ def attachments(attachments)
       @options[:attachments] = attachments
     end
 
+    # MTOM attachments https://www.w3.org/TR/soap12-mtom/
+    def mtom(mtom)
+      @options[:mtom] = mtom
+    end
+
     # Value of the SOAPAction HTTP header.
     def soap_action(soap_action)
       @options[:soap_action] = soap_action
diff --git a/lib/savon/transport/logging.rb b/lib/savon/transport/logging.rb
index 72b96804..eb673091 100644
--- a/lib/savon/transport/logging.rb
+++ b/lib/savon/transport/logging.rb
@@ -53,7 +53,7 @@ def headers_to_log(headers)
       end
 
       def body_to_log(body)
-        LogMessage.new(body, @globals[:filters], @globals[:pretty_print_xml]).to_s
+        LogMessage.new(body, @globals[:filters], @globals[:pretty_print_xml]).to_s.force_encoding(@globals[:encoding])
       end
     end
   end