diff --git a/assets/javascripts/discourse/components/knowledge-explorer-category.js.es6 b/assets/javascripts/discourse/components/knowledge-explorer-category.js.es6
new file mode 100644
index 0000000..3267555
--- /dev/null
+++ b/assets/javascripts/discourse/components/knowledge-explorer-category.js.es6
@@ -0,0 +1,12 @@
+import { default as computed } from "ember-addons/ember-computed-decorators";
+
+export default Ember.Component.extend({
+  @computed("category")
+  categoryName(category) {
+    return this.site.categories.findBy("id", category.id).name;
+  },
+  click() {
+    this.selectCategory(this.category);
+    return false;
+  }
+});
diff --git a/assets/javascripts/discourse/controllers/knowledge-explorer.js.es6 b/assets/javascripts/discourse/controllers/knowledge-explorer.js.es6
index df20433..9a09e29 100644
--- a/assets/javascripts/discourse/controllers/knowledge-explorer.js.es6
+++ b/assets/javascripts/discourse/controllers/knowledge-explorer.js.es6
@@ -16,7 +16,7 @@ function mergeCategories(results) {
 export default Ember.Controller.extend({
   application: Ember.inject.controller(),
   queryParams: {
-    filterCategory: "category",
+    filterCategories: "category",
     filterTags: "tags",
     searchTerm: "search",
     selectedTopic: "topic"
@@ -25,10 +25,11 @@ export default Ember.Controller.extend({
   isLoadingMore: false,
   loadMoreUrl: Ember.computed.alias("model.topics.load_more_url"),
   isTopicLoading: false,
+  categories: Ember.computed.readOnly("model.categories"),
   topics: Ember.computed.alias("model.topics.topic_list.topics"),
   tags: Ember.computed.readOnly("model.tags"),
   filterTags: null,
-  filterCategory: null,
+  filterCategories: null,
   searchTerm: null,
   selectedTopic: null,
   topic: null,
@@ -93,6 +94,26 @@ export default Ember.Controller.extend({
 
       this.send("refreshModel");
     },
+    updateSelectedCategories(category) {
+      let filter = this.filterCategories;
+      if (filter && filter.includes(category.id)) {
+        filter = filter
+          .replace(category.id, "")
+          .replace("|", "|")
+          .replace(/^\|+|\|+$/g, "");
+      } else if (filter) {
+        filter = `${filter}|${category.id}`;
+      } else {
+        filter = category.id;
+      }
+
+      this.setProperties({
+        filterCategories: filter,
+        selectedTopic: null
+      });
+
+      this.send("refreshModel");
+    },
 
     performSearch(term) {
       if (term === "") {
@@ -134,7 +155,7 @@ export default Ember.Controller.extend({
       this.set("isLoading", true);
 
       const params = this.getProperties(
-        "filterCategory",
+        "filterCategories",
         "filterTags",
         "searchTerm"
       );
diff --git a/assets/javascripts/discourse/models/knowledge-explorer.js.es6 b/assets/javascripts/discourse/models/knowledge-explorer.js.es6
index c7b7712..7383f3b 100644
--- a/assets/javascripts/discourse/models/knowledge-explorer.js.es6
+++ b/assets/javascripts/discourse/models/knowledge-explorer.js.es6
@@ -3,6 +3,8 @@ import { ajax } from "discourse/lib/ajax";
 export default {
   list(params) {
     let filters = [];
+    if (params.filterCategories)
+      filters.push(`category=${params.filterCategories}`);
     if (params.filterTags) filters.push(`tags=${params.filterTags}`);
     if (params.searchTerm) filters.push(`search=${params.searchTerm}`);
     if (params.page) filters.push(`page=${params.page}`);
diff --git a/assets/javascripts/discourse/templates/components/knowledge-explorer-category.hbs b/assets/javascripts/discourse/templates/components/knowledge-explorer-category.hbs
new file mode 100644
index 0000000..1f3185f
--- /dev/null
+++ b/assets/javascripts/discourse/templates/components/knowledge-explorer-category.hbs
@@ -0,0 +1,10 @@
+<div class="knowledge-explorer-category {{if category.active 'selected'}}">
+  {{#unless category.active}}
+    {{d-icon "plus"}}
+  {{/unless}}
+  <span class="category-id">{{categoryName}}</span>
+  <span class="category-count">({{category.count}})</span>
+  {{#if category.active}}
+    {{d-icon "times-circle"}}
+  {{/if}}
+</div>
diff --git a/assets/javascripts/discourse/templates/knowledge-explorer.hbs b/assets/javascripts/discourse/templates/knowledge-explorer.hbs
index 0cc3c9c..b729ec6 100644
--- a/assets/javascripts/discourse/templates/knowledge-explorer.hbs
+++ b/assets/javascripts/discourse/templates/knowledge-explorer.hbs
@@ -5,13 +5,25 @@
   }}
   {{#conditional-loading-spinner condition=isLoading}}
     <div class="knowledge-explorer-browse">
-      <div class="knowledge-explorer-tags">
-        {{#each tags as |tag|}}
-          {{knowledge-explorer-tag
-            tag=tag
-            selectTag=(action "updateSelectedTags")
-          }}
-        {{/each}}
+      <div class="knowledge-explorer-filters">
+        <div class="knowledge-explorer-categories">
+          <h3>{{i18n 'knowledge_explorer.categories'}}</h3>
+          {{#each categories as |category|}}
+            {{knowledge-explorer-category
+              category=category
+              selectCategory=(action "updateSelectedCategories")
+            }}
+          {{/each}}
+        </div>
+        <div class="knowledge-explorer-tags">
+          <h3>{{i18n 'knowledge_explorer.tags'}}</h3>
+          {{#each tags as |tag|}}
+            {{knowledge-explorer-tag
+              tag=tag
+              selectTag=(action "updateSelectedTags")
+            }}
+          {{/each}}
+        </div>
       </div>
       {{#if selectedTopic}}
         {{#conditional-loading-spinner condition=isTopicLoading}}
diff --git a/assets/stylesheets/common/knowledge-explorer.scss b/assets/stylesheets/common/knowledge-explorer.scss
index 830d2fa..f7ed760 100644
--- a/assets/stylesheets/common/knowledge-explorer.scss
+++ b/assets/stylesheets/common/knowledge-explorer.scss
@@ -28,13 +28,15 @@
        padding-left: 10px;
      }
    }
-   .knowledge-explorer-tags {
+   .knowledge-explorer-filters {
      flex-basis: 25%;
+   }
+   .knowledge-explorer-tags, .knowledge-explorer-categories {
       padding: 10px 10px 10px 0;
       a {
         color: $primary;
       }
-      .knowledge-explorer-tag {
+      .knowledge-explorer-tag, .knowledge-explorer-category {
         display: flex;
         align-items: center;
         cursor: pointer;
diff --git a/config/locales/client.en.yml b/config/locales/client.en.yml
index ee0e108..c3ced8b 100644
--- a/config/locales/client.en.yml
+++ b/config/locales/client.en.yml
@@ -2,6 +2,8 @@ en:
   js:
     knowledge_explorer:
       title: "Knowledge Explorer"
+      categories: "Categories"
+      tags: "Tags"
       search:
         results: 
           one: "%{count} result found"
diff --git a/lib/knowledge_explorer/query.rb b/lib/knowledge_explorer/query.rb
index 5c8d123..b3e21a8 100644
--- a/lib/knowledge_explorer/query.rb
+++ b/lib/knowledge_explorer/query.rb
@@ -25,7 +25,7 @@ module KnowledgeExplorer
 
       # filter results by selected category
       if @filters[:category].present?
-        results = results.where('category_id IN (?)', @filters[:category])
+        results = results.where('category_id IN (?)', @filters[:category].split('|'))
       end
 
       # filter results by selected tags
@@ -50,6 +50,7 @@ module KnowledgeExplorer
       end
 
       tags = tag_count(results)
+      categories = categories_count(results)
 
       results_length = results.length
 
@@ -75,7 +76,7 @@ module KnowledgeExplorer
         topic_list['load_more_url'] = nil
       end
 
-      { tags: tags, topics: topic_list }
+      { tags: tags, categories: categories, topics: topic_list }
     end
 
     def tag_count(results)
@@ -96,6 +97,22 @@ module KnowledgeExplorer
       tags.sort_by { |tag| [tag[:active] ? 0 : 1, -tag[:count]] }
     end
 
+    def categories_count(results)
+      categories = []
+
+      results.each do |topic|
+        active = @filters[:category].include?(topic.category_id.to_s) if @filters[:category]
+        if categories.none? { |item| item[:id] == topic.category_id }
+          categories << { id: topic.category_id, count: 1, active: active || false }
+        else
+          category_index = categories.index(categories.find { |item| item[:id] == topic.category_id })
+          categories[category_index][:count] += 1
+        end
+      end
+
+      categories.sort_by { |category| [category[:active] ? 0 : 1, -category[:count]] }
+    end
+
     def load_more_url
       filters = []
 
diff --git a/spec/requests/knowledge_explorer_controller_spec.rb b/spec/requests/knowledge_explorer_controller_spec.rb
index af8f767..a6e6cb6 100644
--- a/spec/requests/knowledge_explorer_controller_spec.rb
+++ b/spec/requests/knowledge_explorer_controller_spec.rb
@@ -63,7 +63,7 @@ describe KnowledgeExplorer::KnowledgeExplorerController do
     end
 
     context 'when filtering by tag' do
-      it 'should return a filtered list' do
+      it 'should return a list filtered by tag' do
         get '/knowledge-explorer.json?tags=test'
 
         expect(response.status).to eq(200)
@@ -76,5 +76,40 @@ describe KnowledgeExplorer::KnowledgeExplorerController do
         expect(topics.size).to eq(1)
       end
     end
+
+    context 'when filtering by category' do
+      let!(:category2) { Fabricate(:category) }
+      let!(:topic3) { Fabricate(:topic, category: category2) }
+
+      before do
+        SiteSetting.knowledge_explorer_categories = "#{category.id}|#{category2.id}"
+      end
+
+      it 'should return a list filtered by category' do
+        get "/knowledge-explorer.json?category=#{category2.id}"
+
+        expect(response.status).to eq(200)
+
+        json = JSON.parse(response.body)
+        categories = json['categories']
+        topics = json['topics']['topic_list']['topics']
+
+        expect(categories.size).to eq(1)
+        expect(topics.size).to eq(1)
+      end
+    end
+
+    context 'when searching' do
+      it 'should return a list filtered by search term in title' do
+        get "/knowledge-explorer.json?search=topic 1"
+
+        expect(response.status).to eq(200)
+
+        json = JSON.parse(response.body)
+        topics = json['topics']['topic_list']['topics']
+
+        expect(topics.size).to eq(1)
+      end
+    end
   end
 end