diff --git a/README.md b/README.md
index 58fad43..4f8f30a 100644
--- a/README.md
+++ b/README.md
@@ -24,6 +24,19 @@ my_calendar_name:
         val: # array of values also supported
           - Planning
           - Daily Standup
+   map:
+      - field: summary
+        rules:
+          - field: summary
+            operator: equals
+            val: Busy
+        val: A Meeting
+      - field: summary
+        rules:
+          - field: summary
+            operator: equals
+            val: Tentative
+        val: A Tentative Meeting
 ```
 
 ## Additional Rules
@@ -32,6 +45,10 @@ At the moment rules are pretty simple, supporting only start times, end times, e
 not-equals as that satisfies my use case. To add support for additional rules please extend
 `lib/ical_filter_proxy/filter_rule.rb`. Pull requests welcome.
 
+## Mappings
+
+Fields can be remapped by supplying a set of rules, the field to remap, and the new value.
+
 ## Installing/Running
 
 After you've created a `config.yml` simply bundle and run rackup.
diff --git a/lib/ical_filter_proxy.rb b/lib/ical_filter_proxy.rb
index 43f4109..71cee38 100644
--- a/lib/ical_filter_proxy.rb
+++ b/lib/ical_filter_proxy.rb
@@ -9,6 +9,7 @@
 
 require_relative 'ical_filter_proxy/calendar'
 require_relative 'ical_filter_proxy/filter_rule'
+require_relative 'ical_filter_proxy/mapping'
 require_relative 'ical_filter_proxy/filterable_event_adapter'
 
 module IcalFilterProxy
@@ -18,7 +19,17 @@ def self.filters
 
       filter_config["rules"].each do |rule|
         calendar.add_rule(rule["field"], rule["operator"], rule["val"])
-      end
+      end unless filter_config["rules"].nil?
+
+      filter_config["map"].each do |mapping|
+        rules = []
+
+        mapping["rules"].each do |rule|
+          rules << FilterRule.new(rule["field"], rule["operator"], rule["val"])
+        end
+
+        calendar.add_mapping(mapping["field"], rules, mapping["val"])
+      end unless filter_config["map"].nil?
 
       filters[filter_name] = calendar
     end
diff --git a/lib/ical_filter_proxy/calendar.rb b/lib/ical_filter_proxy/calendar.rb
index d26246f..c8779e0 100644
--- a/lib/ical_filter_proxy/calendar.rb
+++ b/lib/ical_filter_proxy/calendar.rb
@@ -1,6 +1,6 @@
 module IcalFilterProxy
   class Calendar
-    attr_accessor :ical_url, :api_key, :timezone, :filter_rules
+    attr_accessor :ical_url, :api_key, :timezone, :filter_rules, :mappings
 
     def initialize(ical_url, api_key, timezone = 'UTC')
       self.ical_url = ical_url
@@ -8,16 +8,25 @@ def initialize(ical_url, api_key, timezone = 'UTC')
       self.timezone = timezone
 
       self.filter_rules = []
+      self.mappings = []
     end
 
     def add_rule(field, operator, value)
       self.filter_rules << FilterRule.new(field, operator, value)
     end
 
+    def add_mapping(field, rules, value)
+      self.mappings << Mapping.new(field, rules, value)
+    end
+
     def filtered_calendar
       filtered_calendar = Icalendar::Calendar.new
       filtered_events.each do |original_event|
-        filtered_calendar.add_event(original_event)
+        mapped_event = original_event
+        mappings.each do |mapping|
+          mapped_event.send(mapping.field + "=", mapping.value) if mapping_match?(mapping, FilterableEventAdapter.new(original_event, timezone: timezone))
+        end
+        filtered_calendar.add_event(mapped_event)
       end
       filtered_calendar.to_ical
     end
@@ -34,12 +43,16 @@ def filter_match?(event)
       filter_rules.empty? || filter_rules.all? { |rule| rule.match_event?(event) }
     end
 
+    def mapping_match?(mapping, event)
+      mapping.rules.empty? || mapping.rules.all? { |rule| rule.match_event?(event) }
+    end
+
     def original_ics
       Icalendar::Calendar.parse(raw_original_ical).first
     end
 
     def raw_original_ical
-      open(ical_url).read
+      URI.open(ical_url).read
     end
   end
 end
diff --git a/lib/ical_filter_proxy/mapping.rb b/lib/ical_filter_proxy/mapping.rb
new file mode 100644
index 0000000..f16bce1
--- /dev/null
+++ b/lib/ical_filter_proxy/mapping.rb
@@ -0,0 +1,16 @@
+module IcalFilterProxy
+  class Mapping
+
+    attr_accessor :field, :rules, :value
+
+    def initialize(field, rules, value)
+      self.field = field
+      self.rules = rules
+      self.value = value
+    end
+
+    def match_event?(filterable_event)
+      rules.match_event?(filterable_event)
+    end
+  end
+end