diff --git a/src/lib/assets/dash.svg b/src/lib/assets/dash.svg
new file mode 100644
index 00000000..c571a11b
--- /dev/null
+++ b/src/lib/assets/dash.svg
@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" fill="none" viewBox="0 0 16 16"><path stroke="white" stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M4 8h8"/></svg>
\ No newline at end of file
diff --git a/src/lib/components/explorer/FacetCategory.svelte b/src/lib/components/explorer/FacetCategory.svelte
index e93fb371..20f93e2e 100644
--- a/src/lib/components/explorer/FacetCategory.svelte
+++ b/src/lib/components/explorer/FacetCategory.svelte
@@ -2,9 +2,10 @@
   import type { DictionaryFacetResult } from '$lib/models/api/DictionaryResponses';
   import { AccordionItem } from '@skeletonlabs/skeleton';
   import SearchStore from '$lib/stores/Search';
-  import type { Facet } from '$lib/models/Search';
   import { hiddenFacets } from '$lib/services/dictionary';
-  let { updateFacet, selectedFacets } = SearchStore;
+  import FacetItem from './FacetItem.svelte';
+  import type { Facet } from '$lib/models/Search';
+  let { updateFacets, selectedFacets } = SearchStore;
 
   export let facetCategory: DictionaryFacetResult;
   export let facets = facetCategory.facets;
@@ -23,37 +24,100 @@
     (facet) => facet?.categoryRef?.name === facetCategory?.name,
   );
 
-  $: isChecked = (facetToCheck: string) => {
-    return $selectedFacets.some((facet: Facet) => {
-      return facet.name === facetToCheck;
+  function isIndeterminate(facet: Facet): boolean {
+    const atLeastOneChildSelected =
+      facet.children?.some((child) => $selectedFacets.some((f) => f.name === child.name)) ?? false;
+    const isEveryChildSelected = facet.children?.length
+      ? facet.children.every((child) => $selectedFacets.some((f) => f.name === child.name))
+      : false;
+    return atLeastOneChildSelected && !isEveryChildSelected;
+  }
+
+  function isParentFullySelected(facetName: string): boolean {
+    const result = facets.some((parent) => {
+      if (!parent.children || parent.children.length === 0) return false;
+      return parent.children.every(
+        (child) => child.name === facetName || $selectedFacets.some((f) => f.name === child.name),
+      );
     });
-  };
+    return result;
+  }
 
   function getFacetsToDisplay() {
     const hiddenFacetsForCategory = $hiddenFacets[facetCategory.name] || [];
     let facetsToDisplay = facets.filter((f) => !hiddenFacetsForCategory.includes(f.name));
 
-    //Put selected facets at the top
     const selectedFacetsMap = new Map($selectedFacets.map((facet) => [facet.name, facet]));
-    facetsToDisplay = facetsToDisplay.filter((f) => !selectedFacetsMap.has(f.name));
+    const indeterminateFacets = facetsToDisplay.filter(isIndeterminate);
+    const indeterminateMap = new Map(indeterminateFacets.map((facet) => [facet.name, facet]));
 
+    const isChildOfIndeterminate = (facetName: string) => {
+      return indeterminateFacets.some((parent) =>
+        parent.children?.some((child) => child.name === facetName),
+      );
+    };
+
+    // Remove facets that will be added to the top or are children of fully selected parents
+    facetsToDisplay = facetsToDisplay.filter(
+      (f) =>
+        !selectedFacetsMap.has(f.name) &&
+        !isChildOfIndeterminate(f.name) &&
+        !indeterminateMap.has(f.name) &&
+        !isParentFullySelected(f.name),
+    );
+
+    // Add selected facets at the top (excluding children of indeterminate parents and fully selected parents)
     const selectedFacetsForCategory = $selectedFacets.filter(
-      (facet) => facet.category === facetCategory.name,
+      (facet) =>
+        facet.category === facetCategory.name &&
+        !isChildOfIndeterminate(facet.name) &&
+        !isParentFullySelected(facet.name),
     );
     selectedFacetsForCategory.forEach((facet) => {
       facet.count = facets.find((f) => f.name === facet.name)?.count || 0;
     });
 
-    facetsToDisplay.unshift(...selectedFacetsForCategory);
+    //Add parents with all children selected
+    const parentsWithAllChildrenSelected = facets.filter(
+      (f) =>
+        f.children?.length &&
+        f.children.every((child) => $selectedFacets.some((f) => f.name === child.name)),
+    );
+    parentsWithAllChildrenSelected.forEach((facet) => {
+      facet.count = facets.find((f) => f.name === facet.name)?.count || 0;
+    });
+
+    // Add indeterminate facets at the top
+    const indeterminateFacetsForCategory = indeterminateFacets.filter(
+      (facet) => facet.category === facetCategory.name,
+    );
+    indeterminateFacetsForCategory.forEach((facet) => {
+      facet.count = facets.find((f) => f.name === facet.name)?.count || 0;
+    });
+
+    facetsToDisplay.unshift(
+      ...selectedFacetsForCategory,
+      ...parentsWithAllChildrenSelected,
+      ...indeterminateFacetsForCategory,
+    );
+
     if (textFilterValue) {
-      //Filter Facets by searched text
       const lowerFilterValue = textFilterValue.toLowerCase();
-      facetsToDisplay = facetsToDisplay.filter(
-        (facet) =>
+      facetsToDisplay = facetsToDisplay.filter((facet) => {
+        const facetMatches =
           facet.display.toLowerCase().includes(lowerFilterValue) ||
           facet.name.toLowerCase().includes(lowerFilterValue) ||
-          facet.description?.toLowerCase().includes(lowerFilterValue),
-      );
+          facet.description?.toLowerCase().includes(lowerFilterValue);
+
+        const childrenMatch = facet.children?.some(
+          (child) =>
+            child.display.toLowerCase().includes(lowerFilterValue) ||
+            child.name.toLowerCase().includes(lowerFilterValue) ||
+            child.description?.toLowerCase().includes(lowerFilterValue),
+        );
+
+        return facetMatches || childrenMatch;
+      });
     } else if (moreThanTenFacets) {
       // Only show the first n facets
       facetsToDisplay = facetsToDisplay.slice(0, numFacetsToShow);
@@ -77,22 +141,7 @@
         />
       {/if}
       {#each facetsToDisplay as facet}
-        <label data-testId={`facet-${facet.name}-label`} for={facet.name} class="m-1">
-          <input
-            type="checkbox"
-            class="&[aria-disabled=“true”]:opacity-75"
-            id={facet.name}
-            name={facet.name}
-            value={facet}
-            checked={isChecked(facet.name)}
-            disabled={facet.count === 0}
-            aria-checked={isChecked(facet.name)}
-            on:click={() => updateFacet(facet, facetCategory)}
-          />
-          <span class:opacity-75={facet.count === 0}
-            >{`${facet.display} (${facet.count?.toLocaleString()})`}</span
-          >
-        </label>
+        <FacetItem {facet} {facetCategory} facetParent={undefined} {textFilterValue} />
       {/each}
       {#if facets.length > numFacetsToShow && !textFilterValue}
         <button
@@ -116,10 +165,7 @@
       <span class="overflow-hidden text-ellipsis whitespace-nowrap min-w-0">
         {facet.display}
       </span>
-      <button
-        class="chip-close ml-1 flex-shrink-0"
-        on:click={() => updateFacet(facet, facetCategory)}
-      >
+      <button class="chip-close ml-1 flex-shrink-0" on:click={() => updateFacets([facet])}>
         <i class="fa-solid fa-times hover:text-secondary-500"></i>
       </button>
     </span>
diff --git a/src/lib/components/explorer/FacetItem.svelte b/src/lib/components/explorer/FacetItem.svelte
new file mode 100644
index 00000000..860edba8
--- /dev/null
+++ b/src/lib/components/explorer/FacetItem.svelte
@@ -0,0 +1,139 @@
+<script lang="ts">
+  import type { DictionaryFacetResult } from '$lib/models/api/DictionaryResponses';
+  import type { Facet } from '$lib/models/Search';
+  import SearchStore from '$lib/stores/Search';
+  let { updateFacets, selectedFacets } = SearchStore;
+
+  export let facet: Facet;
+  export let facetCategory: DictionaryFacetResult;
+  export let facetParent: Facet | undefined;
+  export let textFilterValue: string | undefined;
+
+  if (facetParent) {
+    facet.parentRef = {
+      name: facetParent.name,
+      display: facetParent.display,
+      description: facetParent.description,
+    };
+  }
+
+  if (facetCategory) {
+    facet.categoryRef = {
+      name: facetCategory.name,
+      display: facetCategory.display,
+      description: facetCategory.description,
+    };
+  }
+
+  let open = false;
+
+  function toggleOpen() {
+    open = !open;
+  }
+
+  function getCurrentlySelectedChildren() {
+    return (
+      facet.children?.filter((child) => $selectedFacets.some((f) => f.name === child.name)) ?? []
+    );
+  }
+
+  function onClick() {
+    if (facet.children && facet.children.length > 0) {
+      if (checkedState(facet.name) === 'indeterminate') {
+        updateFacets(getCurrentlySelectedChildren());
+      } else {
+        updateFacets(facet.children);
+      }
+    } else {
+      updateFacets([facet]);
+    }
+  }
+
+  $: checkedState = (facetToCheck: string) => {
+    const atLeastOneChildSelected =
+      facet.children &&
+      facet.children.some((child) => $selectedFacets.some((f) => f.name === child.name));
+    let isEveryChildSelected = false;
+    if (atLeastOneChildSelected) {
+      isEveryChildSelected =
+        facet.children?.every((child) => $selectedFacets.some((f) => f.name === child.name)) ??
+        false;
+    }
+    const isIndeterminate = atLeastOneChildSelected && !isEveryChildSelected;
+    const isSelected =
+      $selectedFacets.some((facet) => facet.name === facetToCheck) || isEveryChildSelected;
+
+    if (isSelected) return 'true';
+    if (isIndeterminate) return 'indeterminate';
+    return 'false';
+  };
+
+  $: checked = checkedState(facet.name) === 'true';
+  $: facetsToDisplay = facet.children
+    ? [
+        ...facet.children
+          .filter((child) => {
+            const matchesFilter =
+              !textFilterValue ||
+              child.display.toLowerCase().includes(textFilterValue.toLowerCase()) ||
+              child.name.toLowerCase().includes(textFilterValue.toLowerCase()) ||
+              child.description?.toLowerCase().includes(textFilterValue.toLowerCase());
+            return matchesFilter && $selectedFacets.some((f) => f.name === child.name);
+          })
+          .sort((a, b) => (b.count || 0) - (a.count || 0)),
+        ...facet.children
+          .filter((child) => {
+            const matchesFilter =
+              !textFilterValue ||
+              child.display.toLowerCase().includes(textFilterValue.toLowerCase()) ||
+              child.name.toLowerCase().includes(textFilterValue.toLowerCase()) ||
+              child.description?.toLowerCase().includes(textFilterValue.toLowerCase());
+            return matchesFilter && !$selectedFacets.some((f) => f.name === child.name);
+          })
+          .sort((a, b) => (b.count || 0) - (a.count || 0)),
+      ]
+    : [];
+</script>
+
+<label data-testId={`facet-${facet.name}-label`} for={facet.name} class="m-1">
+  {#if facet.children !== undefined && facet.children.length > 0}
+    <button type="button" class="arrow-button" on:click={toggleOpen}>
+      <i class="fa-solid {open ? 'fa-angle-down' : 'fa-angle-right'}"></i>
+    </button>
+  {/if}
+  <input
+    type="checkbox"
+    class={`&[aria-disabled=“true”]:opacity-75 ${checkedState(facet.name)}`}
+    id={facet.name}
+    name={facet.name}
+    value={facet}
+    {checked}
+    disabled={facet.count === 0}
+    aria-checked={checked}
+    on:click={onClick}
+  />
+  <span class:opacity-75={facet.count === 0}
+    >{`${facet.display} (${facet.count?.toLocaleString()})`}</span
+  >
+</label>
+{#if open && facetsToDisplay !== undefined && facetsToDisplay.length > 0}
+  <div class="flex flex-col ml-4">
+    {#each facetsToDisplay as child}
+      <svelte:self facet={child} {facetCategory} facetParent={facet} {textFilterValue} />
+    {/each}
+  </div>
+{/if}
+
+<style lang="postcss">
+  input.indeterminate {
+    background-image: url('$lib/assets/dash.svg');
+    background-size: 100% 100%;
+    background-repeat: no-repeat;
+    background-position: center;
+    background-color: rgb(var(--color-primary-500));
+  }
+
+  .arrow-button {
+    background-color: transparent;
+  }
+</style>
diff --git a/src/lib/models/Search.ts b/src/lib/models/Search.ts
index e234fa6e..bb8c7793 100644
--- a/src/lib/models/Search.ts
+++ b/src/lib/models/Search.ts
@@ -8,6 +8,7 @@ export type Facet = Indexable & {
   children?: Facet[];
   category: string;
   categoryRef?: ShallowFacetCategory;
+  parentRef?: ShallowFacetCategory;
 };
 
 export type ShallowFacetCategory = Pick<Facet, 'name' | 'display' | 'description'>;
diff --git a/src/lib/stores/Search.ts b/src/lib/stores/Search.ts
index 9f19dda5..1819f49a 100644
--- a/src/lib/stores/Search.ts
+++ b/src/lib/stores/Search.ts
@@ -1,9 +1,6 @@
 import { get, writable, type Writable } from 'svelte/store';
 import { type Facet, type SearchResult } from '$lib/models/Search';
-import type {
-  DictionaryConceptResult,
-  DictionaryFacetResult,
-} from '$lib/models/api/DictionaryResponses';
+import type { DictionaryConceptResult } from '$lib/models/api/DictionaryResponses';
 import type { State } from '@vincjo/datatables/remote';
 import { searchDictionary } from '$lib/services/dictionary';
 
@@ -38,30 +35,18 @@ async function search(searchTerm: string, facets: Facet[], state?: State): Promi
   }
 }
 
-async function updateFacet(newFacet: Facet, facetCategory: DictionaryFacetResult | undefined) {
-  if (facetCategory) {
-    newFacet.categoryRef = {
-      display: facetCategory.display,
-      name: facetCategory.name,
-      description: facetCategory.description,
-    };
-  }
-  try {
-    selectedFacets.update((facets) => {
-      const index = facets.findIndex((facet) => facet.name === newFacet.name);
-      if (index === -1) {
-        facets.push(newFacet);
-      } else {
-        facets.splice(index, 1);
-      }
-      //For reactivity and sorting
-      selectedFacets.set(get(selectedFacets).sort((a, b) => b.count - a.count));
-      return facets;
-    });
-  } catch (e) {
-    console.error(e);
-    return;
-  }
+async function updateFacets(facetsToUpdate: Facet[]) {
+  const currentFacets = get(selectedFacets);
+  facetsToUpdate.forEach((facet) => {
+    const facetIndex = currentFacets.findIndex((f) => f.name === facet.name);
+    if (facetIndex !== -1) {
+      currentFacets.splice(facetIndex, 1);
+    } else {
+      currentFacets.push(facet);
+    }
+  });
+
+  selectedFacets.set(currentFacets.sort((a, b) => b.count - a.count));
 }
 
 export function resetSearch() {
@@ -75,6 +60,6 @@ export default {
   searchTerm,
   error,
   search,
-  updateFacet,
+  updateFacets,
   resetSearch,
 };