diff --git a/app/controllers/accounts/requests_controller.rb b/app/controllers/accounts/requests_controller.rb
index 642f9366..f25101ab 100644
--- a/app/controllers/accounts/requests_controller.rb
+++ b/app/controllers/accounts/requests_controller.rb
@@ -6,5 +6,16 @@ class Accounts::RequestsController < ApplicationController
   def index
     @pending_requests = current_user.requests.pending
     @requests = current_user.requests.closed
+
+    respond_to do |format|
+      format.html
+
+      # Return all requests in the XML, sorted by creation date
+      format.xml {
+        render :xml => (@pending_requests + @requests).sort do |a, b|
+          a.created_at <=> b.created_at
+        end
+      }
+    end
   end
 end
diff --git a/app/controllers/contests_controller.rb b/app/controllers/contests_controller.rb
index 3d8a37e0..68e239d9 100644
--- a/app/controllers/contests_controller.rb
+++ b/app/controllers/contests_controller.rb
@@ -1,3 +1,5 @@
+require 'builder'
+
 class ContestsController < ApplicationController
   def permitted_params
     @_permitted_params ||= begin
@@ -18,7 +20,7 @@ def index
       authorize Contest.new, :manage?
       @contests = Contest.order("end_time DESC")
     end
-    
+
     respond_to do |format|
       format.html # index.html.erb
     end
@@ -42,6 +44,11 @@ def browse
     else
       raise Pundit::NotAuthorizedError
     end
+
+    respond_to do |format|
+      format.html
+      format.xml { render :xml => @contests.to_xml(:user => current_user) }
+    end
   end
 
   # GET /contests/1
@@ -61,7 +68,10 @@ def show
       @contest_message = "You have not started this contest."
     end
 
-    render :layout => 'contest'
+    respond_to do |format|
+      format.html { render :layout => 'contest' }
+      format.xml { render :xml => @contest.to_xml(:user => current_user) }
+    end
   end
 
   def info
diff --git a/app/controllers/groups_controller.rb b/app/controllers/groups_controller.rb
index 6165b184..0c27db5d 100644
--- a/app/controllers/groups_controller.rb
+++ b/app/controllers/groups_controller.rb
@@ -59,7 +59,10 @@ def show
     @group = Group.find(params[:id])
     if policy(@group).access?
       @problem_set_associations = @group.problem_set_associations
-      render :layout => "group"
+      respond_to do |format|
+        format.html { render :layout => "group" }
+        format.xml { render :xml => @group }
+      end
     else
       redirect_to info_group_path(@group)
     end
@@ -73,8 +76,8 @@ def contests
       format.html { render :layout => "group" }
     end
   end
-  
-  def info 
+
+  def info
     @group = Group.find(params[:id])
     authorize @group, :show?
     respond_to do |format|
diff --git a/app/controllers/problems_controller.rb b/app/controllers/problems_controller.rb
index b345ac7f..1440a9cc 100644
--- a/app/controllers/problems_controller.rb
+++ b/app/controllers/problems_controller.rb
@@ -50,6 +50,7 @@ def index
 
     respond_to do |format|
       format.html # index.html.erb
+      format.xml { render :xml => @problems }
     end
   end
 
@@ -73,6 +74,7 @@ def show
 
     respond_to do |format|
       format.html { render :layout => "problem" }
+      format.xml { render :xml => @problem }
     end
 
     if user_signed_in?
@@ -115,7 +117,7 @@ def submissions
       start_time = current_user.contest_relations.joins(:contest => {:problem_set => :problems}).where{(started_at <= DateTime.now) & (finish_at > DateTime.now) & (contest.problem_set.problems.id == my{params[:id]})}.minimum(:started_at)
       @submissions = @problem.submission_history(current_user,start_time)
     end
-    
+
     respond_to do |format|
       format.html { render :layout => "problem" }
     end
@@ -225,7 +227,7 @@ def create
   def update
     @problem = Problem.find(params[:id])
     authorize @problem, :update?
-    
+
     @problem.assign_attributes(permitted_params)
     respond_to do |format|
       if validate(@problem) && @problem.save
diff --git a/app/controllers/user_controller.rb b/app/controllers/user_controller.rb
index d8de9ddf..de2bea53 100644
--- a/app/controllers/user_controller.rb
+++ b/app/controllers/user_controller.rb
@@ -21,13 +21,13 @@ def visible_attributes
   def show
     @user = User.find(params[:id])
     authorize @user, :show?
-    @solved_problems = @user.user_problem_relations.where(ranked_score: 100).joins(:problem).select([:problem_id, :ranked_submission_id, {problem: :name}]).order("problems.name")
+    @solved_problems = @user.solved_problems
 
     @user_presenter = UserPresenter.new(@user).permit!(*visible_attributes)
 
     respond_to do |format|
       format.html
-      format.xml {render :xml => @user }
+      format.xml {render :xml => @user, :user => current_user }
     end
   end
 
diff --git a/app/models/contest.rb b/app/models/contest.rb
index 9edd6d23..332f02be 100644
--- a/app/models/contest.rb
+++ b/app/models/contest.rb
@@ -117,7 +117,7 @@ def status
     return "Running" if is_running?
     return finalized? ? "Finalized" : "Preliminary"
   end
-  
+
   def status_text(user_id)
     return "The contest has ended." if ended?
 
@@ -166,4 +166,38 @@ def max_extra_time
     (duration*3600).to_i
   end
 
+  def to_xml(opts={})
+    opts[:exclude] ||= [:startcode]
+
+    super(opts) do |xml|
+      if opts[:user] then
+        policy = Pundit.policy(opts[:user], self)
+
+        has_contestants = policy.contestants?
+        has_scoreboard = policy.scoreboard?
+
+        if policy.contestants? then
+          XmlUtil.serialize_id_list xml, 'contestants', contestants
+        end
+
+        if policy.scoreboard? then
+          # TODO: Include scoreboard info
+
+          XmlUtil.serialize_list xml, 'problems', problem_set.problems do |problem|
+            association = problem_associations.find {|i| i.problem_id == problem.id}
+            xml.id(
+              problem.id,
+              'type' => ActiveSupport::XmlMini::TYPE_NAMES[association.weighting.class.name],
+              'weighting' => association.weighting,
+            )
+          end
+        end
+
+        if policy.manage? then
+          XmlUtil.serialize_id_list xml, 'groups', groups
+          XmlUtil.serialize_id_list xml, 'registrants', registrants
+        end
+      end
+    end
+  end
 end
diff --git a/app/models/group.rb b/app/models/group.rb
index 0ac34b37..f4bcf234 100644
--- a/app/models/group.rb
+++ b/app/models/group.rb
@@ -54,5 +54,13 @@ def apply!(current_user, user = nil)
   def invite!(user, current_user)
     Request.create(:requester => current_user, :subject => self, :verb => :invite, :target => user, :requestee => user)
   end
+
+  def to_xml(opts={})
+    # No sensitive data
+    super(opts) do |xml|
+      XmlUtil.serialize_id_list xml, 'contests', contests
+      XmlUtil.serialize_id_list xml, 'problem-sets', problem_sets
+    end
+  end
 end
 
diff --git a/app/models/problem.rb b/app/models/problem.rb
index 9c92cfc9..67a57519 100644
--- a/app/models/problem.rb
+++ b/app/models/problem.rb
@@ -72,7 +72,7 @@ def get_highest_scoring_submission(user, from = DateTime.new(1), to = DateTime.n
   def get_score(user, from = DateTime.new(1), to = DateTime.now)
     subs = self.submissions.find(:all, :limit => 1, :order => "score DESC", :conditions => ["created_at between ? and ? and user_id = ?", from, to, user])
     scores = subs.map {|s| s.score}
-    return scores.max 
+    return scores.max
   end
 
   def submission_history(user, from = DateTime.new(1), to = DateTime.now)
@@ -108,4 +108,24 @@ def weighted_score
     return nil if self.points.nil?
     self.points * self.weighting / self.maximum_points
   end
+
+  def to_xml(opts={})
+    # hide e.g. test submission stats
+    opts[:only] ||= [:id, :name, :statement, :input, :output, :memory_limit, :time_limit, :owner_id, :created_at, :updated_at]
+
+    super(opts) do |xml|
+      XmlUtil.serialize_id_list xml, 'contests', contests
+      XmlUtil.serialize_id_list xml, 'groups', groups
+      XmlUtil.serialize_id_list xml, 'problem-sets', problem_sets
+
+      XmlUtil.serialize_list xml, 'sample-cases', sample_cases do |sample|
+        xml.tag! 'sample-case' do
+          XmlUtil.tag xml, 'input', sample.input
+          XmlUtil.tag xml, 'output', sample.output
+        end
+      end
+
+      # TODO: Possibly nice to include submission ids here if user is an admin?
+    end
+  end
 end
diff --git a/app/models/problem_set.rb b/app/models/problem_set.rb
index b1f473b5..2f274836 100644
--- a/app/models/problem_set.rb
+++ b/app/models/problem_set.rb
@@ -36,4 +36,14 @@ def for_group_user? u_id
   def total_weighting
     problem_associations.sum(:weighting)
   end
+
+  def to_xml(opts={})
+    opts[:only] ||= [:id, :name, :owner_id, :created_at, :updated_at]
+
+    super(opts) do |xml|
+      XmlUtil.serialize_id_list xml, 'contests', contests
+      XmlUtil.serialize_id_list xml, 'groups', groups
+      XmlUtil.serialize_id_list xml, 'problems', problems
+    end
+  end
 end
diff --git a/app/models/request.rb b/app/models/request.rb
index b4b2e6b3..7cf3e72b 100644
--- a/app/models/request.rb
+++ b/app/models/request.rb
@@ -1,6 +1,6 @@
 class Request < ActiveRecord::Base
   include ActiveModel::ForbiddenAttributesProtection
-  
+
   belongs_to :requester, :class_name => :User # entity that initiated request
   belongs_to :subject, :polymorphic => true # subject controlled by requester
   # verb # action applying subject to target
@@ -42,4 +42,18 @@ def cancel!
     self.status = STATUS[:cancelled]
     self.save
   end
+
+  def to_xml(opts={})
+    if self.expired_at == Float::INFINITY then
+      # `expired_at` has the value Float::INFINITY when the request hasn't expired,
+      # and the XML formatter explodes when it encounters that value. Adding :expired_at
+      # to opts[:exclude] is the obvious solution, but for reasons unknown to me it does
+      # not appear to work as expected. Changing `expired_at` to some other value (which isn't
+      # a datetime) will result in an empty tag being emitted with a `nil="true"` attribute
+      # which seems like the best solution after just omitting the tag entirely.`
+      self.expired_at = 0
+    end
+
+    super(opts)
+  end
 end
diff --git a/app/models/submission.rb b/app/models/submission.rb
index 644c04ab..e80cf841 100644
--- a/app/models/submission.rb
+++ b/app/models/submission.rb
@@ -1,6 +1,6 @@
 class Submission < ActiveRecord::Base
   include ActiveModel::ForbiddenAttributesProtection
-  
+
   belongs_to :user
   belongs_to :problem
   has_many :contest_scores
@@ -9,7 +9,7 @@ class Submission < ActiveRecord::Base
   def user_problem_relation
     UserProblemRelation.where(:user_id => user_id, :problem_id => problem_id).first_or_create!
   end
-  
+
   validates :source, :presence => true
   validate do |submission|
     errors.add :language_id, "Invalid language specified" if submission.language.nil?
@@ -199,5 +199,11 @@ def update_test_messages
     end
   end
 
+  def to_xml(opts={})
+    # hiding e.g. judge log
+    opts[:only] ||= [:id, :source, :score, :user_id, :problem_id, :created_at, :updated_at, :input, :output, :language_id, :judged_at, :evaluation]
+
+    super(opts)
+  end
 end
 
diff --git a/app/models/user.rb b/app/models/user.rb
index c50b77c0..6e1a0456 100644
--- a/app/models/user.rb
+++ b/app/models/user.rb
@@ -173,6 +173,10 @@ def school=(value)
     end
   end
 
+  def solved_problems
+    self.user_problem_relations.where(ranked_score: 100).joins(:problem).select([:problem_id, :ranked_submission_id, {problem: :name}]).order("problems.name")
+  end
+
   def estimated_year_level(on_this_date = DateTime.now)
     if school_graduation.nil? || school_graduation <= on_this_date
       nil
@@ -187,4 +191,25 @@ def estimated_year_level(on_this_date = DateTime.now)
     end
   end
 
+  def to_xml(opts={})
+    default_fields = [:id, :created_at, :updated_at, :brownie_points, :username, :avatar]
+    if opts[:user] then
+      if Pundit.policy(opts[:user], self).inspect? then
+        default_fields.append(:email)
+        default_fields.append(:name)
+      end
+    end
+    opts[:only] ||= default_fields
+
+    super(opts) do |xml|
+      if opts[:user] then
+        if Pundit.policy(opts[:user], self).inspect? then
+          XmlUtil.serialize_id_list xml, 'groups', groups
+          XmlUtil.serialize_list xml, 'solved-problems', solved_problems do |association|
+            XmlUtil.tag xml, 'id', association.problem_id
+          end
+        end
+      end
+    end
+  end
 end
diff --git a/app/services/xml_util.rb b/app/services/xml_util.rb
new file mode 100644
index 00000000..d6f4b455
--- /dev/null
+++ b/app/services/xml_util.rb
@@ -0,0 +1,21 @@
+module XmlUtil
+  def self.serialize_list builder, name, docs
+    array_type = ActiveSupport::XmlMini::TYPE_NAMES['Array']
+    builder.tag!(name, 'count' => docs.count, 'type' => array_type) do
+      docs.each do |doc| yield doc end
+    end
+  end
+
+  def self.serialize_id_list builder, name, docs
+    array_type = ActiveSupport::XmlMini::TYPE_NAMES['Array']
+
+    XmlUtil.serialize_list builder, name, docs do |doc|
+      XmlUtil.tag builder, 'id', doc.id
+    end
+  end
+
+  # Wrapper around ActiveSupport's to_tag method as the original is pretty long
+  def self.tag builder, name, value
+    ActiveSupport::XmlMini.to_tag(name, value, {:builder => builder})
+  end
+end