diff --git a/Ghidra/Features/Base/src/main/help/help/topics/DataTypeManagerPlugin/data_type_manager_window.html b/Ghidra/Features/Base/src/main/help/help/topics/DataTypeManagerPlugin/data_type_manager_window.html
index 6c57b766da..ec86c30414 100644
--- a/Ghidra/Features/Base/src/main/help/help/topics/DataTypeManagerPlugin/data_type_manager_window.html
+++ b/Ghidra/Features/Base/src/main/help/help/topics/DataTypeManagerPlugin/data_type_manager_window.html
@@ -628,12 +628,15 @@
           Types</H3>
 
           <BLOCKQUOTE>
-            <P>You can apply all function signature data types from an archive to the currently
-            open Program. Function signature definitions can also be applied from the currently
-            open program's defined data types. Applying data types from the program is useful when
+            <P>You can apply all function definition data types from an archive or selected category to the currently
+            open Program.  This can be done from the Data Type Manager tree
+            by selecting the <I><B>Apply Function Data Types</B></I> popup action
+            for a selected Archive or Category node.
+            Function definitions can also be applied from the currently open program's defined data types.  
+            Applying data types from the program is useful when
             source header files have been parsed into the program instead of an archive. This
-            action attempts to match the function definition with user defined symbol names in the
-            Program. When a match is found, the <I><B>Apply All</B></I> action does one of the
+            action attempts to match the function definition with symbol names in the
+            Program. When a match is found, the <I><B>Apply Function Data Types</B></I> action does one of the
             following:<BR>
             </P>
 
@@ -667,8 +670,8 @@
               within the selection will have their signatures captured.</LI>
             </UL>
 
-            <P>Once you have captured the function data types to an archive, you can use the <A
-            href="#Apply_All">Apply Function Data Types</A> to apply the function definition data
+            <P>Once you have captured the function definitions to an archive, you can use the <A
+            href="#Apply_Function_Data_Types">Apply Function Data Types</A> action to apply the function definition data
             types to another program.</P>
           </BLOCKQUOTE>
 
diff --git a/Ghidra/Features/Base/src/main/java/ghidra/app/cmd/function/ApplyFunctionDataTypesCmd.java b/Ghidra/Features/Base/src/main/java/ghidra/app/cmd/function/ApplyFunctionDataTypesCmd.java
index c6d5b54420..12d02d0266 100644
--- a/Ghidra/Features/Base/src/main/java/ghidra/app/cmd/function/ApplyFunctionDataTypesCmd.java
+++ b/Ghidra/Features/Base/src/main/java/ghidra/app/cmd/function/ApplyFunctionDataTypesCmd.java
@@ -21,12 +21,14 @@ import ghidra.app.cmd.disassemble.DisassembleCommand;
 import ghidra.app.util.PseudoDisassembler;
 import ghidra.framework.cmd.BackgroundCommand;
 import ghidra.framework.model.DomainObject;
-import ghidra.program.model.address.*;
+import ghidra.program.model.address.Address;
+import ghidra.program.model.address.AddressSetView;
 import ghidra.program.model.data.*;
 import ghidra.program.model.listing.*;
 import ghidra.program.model.mem.MemoryBlock;
 import ghidra.program.model.symbol.*;
 import ghidra.util.Msg;
+import ghidra.util.exception.CancelledException;
 import ghidra.util.task.TaskMonitor;
 
 /**
@@ -37,12 +39,11 @@ import ghidra.util.task.TaskMonitor;
 public class ApplyFunctionDataTypesCmd extends BackgroundCommand {
 	private Program program;
 	private BookmarkManager bookmarkMgr;
-	private List<DataTypeManager> managers;
+	private List<Category> sourceCategories;
 	private AddressSetView addresses;
 	private SourceType source;
 	private boolean alwaysReplace;
 	private boolean createBookmarksEnabled;
-	private Map<String, FunctionDefinition> functionNameMap = new HashMap<>();
 
 	/**
 	 * Constructs a new command to apply all function signature data types
@@ -61,13 +62,45 @@ public class ApplyFunctionDataTypesCmd extends BackgroundCommand {
 	public ApplyFunctionDataTypesCmd(List<DataTypeManager> managers, AddressSetView set,
 			SourceType source, boolean alwaysReplace, boolean createBookmarksEnabled) {
 		super("Apply Function Data Types", true, false, false);
-		this.managers = managers;
+		this.sourceCategories = getRootCategories(managers);
 		this.addresses = set;
 		this.source = source;
 		this.alwaysReplace = alwaysReplace;
 		this.createBookmarksEnabled = createBookmarksEnabled;
 	}
 
+	/**
+	 * Constructs a new command to apply all function signature data types
+	 * in the given data type category (includes all subcategories).
+	 * 
+	 * @param sourceCategory datatype category containing the function signature data types
+	 * @param set set of addresses containing labels to match against function names.
+	 * 			  The addresses must not already be included in the body of any existing function.
+	 *  		  If null, all symbols will be processed
+	 * @param source the source of this command.
+	 * @param alwaysReplace true to always replace the existing function signature with the
+	 * 						function signature data type.
+	 * @param createBookmarksEnabled true to create a bookmark when a function signature
+	 * 								 has been applied.
+	 */
+	public ApplyFunctionDataTypesCmd(Category sourceCategory, AddressSetView set,
+			SourceType source, boolean alwaysReplace, boolean createBookmarksEnabled) {
+		super("Apply Function Data Types", true, false, false);
+		this.sourceCategories = List.of(sourceCategory);
+		this.addresses = set;
+		this.source = source;
+		this.alwaysReplace = alwaysReplace;
+		this.createBookmarksEnabled = createBookmarksEnabled;
+	}
+
+	private static List<Category> getRootCategories(List<DataTypeManager> managers) {
+		List<Category> roots = new ArrayList<>();
+		for (DataTypeManager dtm : managers) {
+			roots.add(dtm.getRootCategory());
+		}
+		return roots;
+	}
+
 	@Override
 	public boolean applyTo(DomainObject obj, TaskMonitor monitor) {
 		program = (Program) obj;
@@ -77,7 +110,12 @@ public class ApplyFunctionDataTypesCmd extends BackgroundCommand {
 
 		Map<String, List<Symbol>> symbolMap = createSymMap();
 
-		applyDataTypes(monitor, symbolMap);
+		try {
+			applyFunctionDefinitions(monitor, symbolMap);
+		}
+		catch (CancelledException e) {
+			// ignore and return
+		}
 
 		return true;
 	}
@@ -136,39 +174,23 @@ public class ApplyFunctionDataTypesCmd extends BackgroundCommand {
 	}
 
 	/**
-	 * Apply all descendants starting at node.
+	 * Apply all descendants starting at each category node.
+	 * @param monitor task monitor
+	 * @param symbolMap symbol map where possible function definitions may be applied
+	 * @throws CancelledException if task cancelled
 	 */
-	private void applyDataTypes(TaskMonitor monitor, Map<String, List<Symbol>> symbolMap) {
-
-		for (DataTypeManager dataTypeManager : managers) {
-			Iterator<DataType> iter = dataTypeManager.getAllDataTypes();
-			while (iter.hasNext()) {
-				if (monitor.isCancelled()) {
-					return;
-				}
-
-				DataType dt = iter.next();
-				if (!(dt instanceof FunctionDefinition)) {
-					continue;
-				}
-
-				FunctionDefinition fdef = (FunctionDefinition) dt;
-				String name = fdef.getName();
-				if (functionNameMap.containsKey(name)) {
-					FunctionDefinition dupeFdef = functionNameMap.get(name);
-					if (!fdef.isEquivalent(dupeFdef)) {
-						// set the functionDef to null to mark dupes
-						functionNameMap.put(name, null);
-					}
-				}
-				else {
-					functionNameMap.put(name, fdef);
-				}
-			}
+	private void applyFunctionDefinitions(TaskMonitor monitor,
+			Map<String, List<Symbol>> symbolMap) throws CancelledException {
 
+		Map<String, FunctionDefinition> functionNameMap = new HashMap<>();
+		for (Category cat : sourceCategories) {
+			collectFunctionDefinitions(cat, monitor, functionNameMap);
 		}
+
 		monitor.initialize(functionNameMap.size());
 		for (String functionName : functionNameMap.keySet()) {
+			monitor.checkCanceled();
+
 			FunctionDefinition fdef = functionNameMap.get(functionName);
 			checkForSymbol(monitor, functionName, fdef, symbolMap, null);
 
@@ -180,6 +202,36 @@ public class ApplyFunctionDataTypesCmd extends BackgroundCommand {
 
 	}
 
+	private void collectFunctionDefinitions(Category cat, TaskMonitor monitor,
+			Map<String, FunctionDefinition> functionNameMap) throws CancelledException {
+
+		monitor.checkCanceled();
+
+		for (DataType dt : cat.getDataTypes()) {
+			monitor.checkCanceled();
+			if (!(dt instanceof FunctionDefinition)) {
+				continue;
+			}
+
+			FunctionDefinition fdef = (FunctionDefinition) dt;
+			String name = fdef.getName();
+			if (functionNameMap.containsKey(name)) {
+				FunctionDefinition dupeFdef = functionNameMap.get(name);
+				if (!fdef.isEquivalent(dupeFdef)) {
+					// set the functionDef to null to mark dupes
+					functionNameMap.put(name, null);
+				}
+			}
+			else {
+				functionNameMap.put(name, fdef);
+			}
+		}
+
+		for (Category subcat : cat.getCategories()) {
+			collectFunctionDefinitions(subcat, monitor, functionNameMap);
+		}
+	}
+
 	private void checkForSymbol(TaskMonitor monitor, String functionName, FunctionDefinition fdef,
 			Map<String, List<Symbol>> symbolMap, String prefix) {
 
@@ -330,7 +382,7 @@ public class ApplyFunctionDataTypesCmd extends BackgroundCommand {
 	}
 
 	private SourceType getMostTrustedParameterSource(Function func) {
-		SourceType highestSource = SourceType.DEFAULT;
+		SourceType highestSource = func.getSignatureSource();
 		Parameter[] parameters = func.getParameters();
 		for (Parameter parameter : parameters) {
 			SourceType paramSource = parameter.getSource();
diff --git a/Ghidra/Features/Base/src/main/java/ghidra/app/plugin/core/datamgr/actions/ApplyFunctionDataTypesAction.java b/Ghidra/Features/Base/src/main/java/ghidra/app/plugin/core/datamgr/actions/ApplyFunctionDataTypesAction.java
index 5d466e5996..93ee14a6f3 100644
--- a/Ghidra/Features/Base/src/main/java/ghidra/app/plugin/core/datamgr/actions/ApplyFunctionDataTypesAction.java
+++ b/Ghidra/Features/Base/src/main/java/ghidra/app/plugin/core/datamgr/actions/ApplyFunctionDataTypesAction.java
@@ -15,9 +15,6 @@
  */
 package ghidra.app.plugin.core.datamgr.actions;
 
-import java.util.ArrayList;
-import java.util.List;
-
 import javax.swing.tree.TreePath;
 
 import docking.ActionContext;
@@ -30,7 +27,6 @@ import ghidra.app.plugin.core.datamgr.DataTypeManagerPlugin;
 import ghidra.app.plugin.core.datamgr.DataTypesActionContext;
 import ghidra.app.plugin.core.datamgr.tree.*;
 import ghidra.framework.plugintool.PluginTool;
-import ghidra.program.model.data.DataTypeManager;
 import ghidra.program.model.listing.Program;
 import ghidra.program.model.symbol.SourceType;
 
@@ -66,6 +62,12 @@ public class ApplyFunctionDataTypesAction extends DockingAction {
 		}
 
 		GTreeNode node = (GTreeNode) selectionPaths[0].getLastPathComponent();
+
+		if (node instanceof CategoryNode) {
+			CategoryNode catNode = (CategoryNode) node;
+			node = catNode.getArchiveNode();
+		}
+
 		return (node instanceof FileArchiveNode) || (node instanceof ProjectArchiveNode) ||
 			(node instanceof ProgramArchiveNode);
 	}
@@ -74,14 +76,12 @@ public class ApplyFunctionDataTypesAction extends DockingAction {
 	public void actionPerformed(ActionContext context) {
 		GTree gTree = (GTree) context.getContextObject();
 		TreePath selectionPath = gTree.getSelectionPath();
-		ArchiveNode node = (ArchiveNode) selectionPath.getLastPathComponent();
+		CategoryNode node = (CategoryNode) selectionPath.getLastPathComponent();
 
 		Program program = plugin.getProgram();
-		DataTypeManager manager = node.getArchive().getDataTypeManager();
-		List<DataTypeManager> managerList = new ArrayList<DataTypeManager>();
-		managerList.add(manager);
 		ApplyFunctionDataTypesCmd cmd =
-			new ApplyFunctionDataTypesCmd(managerList, null, SourceType.USER_DEFINED, true, true);
+			new ApplyFunctionDataTypesCmd(node.getCategory(), null, SourceType.USER_DEFINED, true,
+				true);
 		PluginTool tool = plugin.getTool();
 		tool.executeBackgroundCommand(cmd, program);
 	}
diff --git a/GhidraDocs/GhidraClass/Intermediate/Intermediate_Ghidra_Student_Guide.html b/GhidraDocs/GhidraClass/Intermediate/Intermediate_Ghidra_Student_Guide.html
index 56a13e217d..182d4caccc 100644
--- a/GhidraDocs/GhidraClass/Intermediate/Intermediate_Ghidra_Student_Guide.html
+++ b/GhidraDocs/GhidraClass/Intermediate/Intermediate_Ghidra_Student_Guide.html
@@ -208,7 +208,8 @@
     <ul>
 	<li>Users can create a function definition data type for function signatures they might want apply again in a new program for a particular named function. To do this, click on a function signature and choose Function->Create Function Definition from the Listing right mouse menu.</li>
       <li>Users can create function definitions for their whole program by choosing Capture Function Data Types from the Data Type Manager right mouse menu.</li>
-     <li>In new program, apply function signature by right mousing on appropriate folder in Data Type Manager and choosing Apply Function Data Types</li>
+     <li>In new program, apply function signatures by right mouse-clicking on an appropriate category folder in the Data Type Manager and 
+     choosing <b>Apply Function Data Types</b> from the popup menu.</li>
 
     </ul>
   </ul>