diff --git a/SourceGenWPF/MainController.cs b/SourceGenWPF/MainController.cs
index 3988c11..22050ab 100644
--- a/SourceGenWPF/MainController.cs
+++ b/SourceGenWPF/MainController.cs
@@ -24,6 +24,7 @@ using Asm65;
 using CommonUtil;
 using SourceGenWPF.ProjWin;
 using System.Web.Script.Serialization;
+using System.Text;
 
 namespace SourceGenWPF {
     /// <summary>
@@ -1013,6 +1014,12 @@ namespace SourceGenWPF {
             return mProject != null;
         }
 
+        public void SelectionChanged(out SelectionState newState) {
+            newState = UpdateSelectionState();
+
+            UpdateInfoPanel();
+        }
+
         /// <summary>
         /// Gathered facts about the current selection.  Recalculated whenever the selection
         /// changes.
@@ -1282,5 +1289,228 @@ namespace SourceGenWPF {
         }
 
         #endregion Main window UI event handlers
+
+        #region Info panel
+
+        private void UpdateInfoPanel() {
+            if (mMainWin.GetSelectionCount() != 1) {
+                // Nothing selected, or multiple lines selected.
+                mMainWin.InfoBoxContents = string.Empty;
+                return;
+            }
+            int lineIndex = mMainWin.GetFirstSelectedIndex();
+            LineListGen.Line line = CodeListGen[lineIndex];
+            StringBuilder sb = new StringBuilder(250);
+
+            // TODO(someday): this should be made easier to localize
+            string lineTypeStr;
+            string extraStr = string.Empty;
+            switch (line.LineType) {
+                case LineListGen.Line.Type.Code:
+                    lineTypeStr = "code";
+                    break;
+                case LineListGen.Line.Type.Data:
+                    if (mProject.GetAnattrib(line.FileOffset).IsInlineData) {
+                        lineTypeStr = "inline data";
+                    } else {
+                        lineTypeStr = "data";
+                    }
+                    break;
+                case LineListGen.Line.Type.LongComment:
+                    lineTypeStr = "comment";
+                    break;
+                case LineListGen.Line.Type.Note:
+                    lineTypeStr = "note";
+                    break;
+                case LineListGen.Line.Type.Blank:
+                    lineTypeStr = "blank line";
+                    //lineTypeStr = "blank line (+" +
+                    //    mOutputFormatter.FormatOffset24(line.FileOffset) + ")";
+                    break;
+                case LineListGen.Line.Type.OrgDirective:
+                    lineTypeStr = "address directive";
+                    break;
+                case LineListGen.Line.Type.RegWidthDirective:
+                    lineTypeStr = "register width directive";
+                    break;
+                case LineListGen.Line.Type.EquDirective: {
+                        lineTypeStr = "equate";
+                        int symIndex = LineListGen.DefSymIndexFromOffset(line.FileOffset);
+                        DefSymbol defSym = mProject.ActiveDefSymbolList[symIndex];
+                        string sourceStr;
+                        if (defSym.SymbolSource == Symbol.Source.Project) {
+                            sourceStr = "project symbol definition";
+                        } else if (defSym.SymbolSource == Symbol.Source.Platform) {
+                            sourceStr = "platform symbol file";
+                        } else {
+                            sourceStr = "???";
+                        }
+                        extraStr = "Source: " + sourceStr;
+                    }
+                    break;
+                default:
+                    lineTypeStr = "???";
+                    break;
+            }
+
+            // For anything that isn't code or data, show something simple and bail.
+            if (line.OffsetSpan == 0) {
+                sb.AppendFormat(Res.Strings.INFO_LINE_SUM_NON_FMT,
+                    lineIndex, lineTypeStr);
+#if DEBUG
+                sb.Append(" [offset=+" + line.FileOffset.ToString("x6") + "]");
+#endif
+                if (!string.IsNullOrEmpty(extraStr)) {
+                    sb.Append("\r\n\r\n");
+                    sb.Append(extraStr);
+                }
+                mMainWin.InfoBoxContents = sb.ToString();
+                return;
+            }
+            Debug.Assert(line.IsCodeOrData);
+
+            Anattrib attr = mProject.GetAnattrib(line.FileOffset);
+
+            // Show number of bytes of code/data.
+            if (line.OffsetSpan == 1) {
+                sb.AppendFormat(Res.Strings.INFO_LINE_SUM_SINGULAR_FMT,
+                    lineIndex, line.OffsetSpan, lineTypeStr);
+            } else {
+                sb.AppendFormat(Res.Strings.INFO_LINE_SUM_PLURAL_FMT,
+                    lineIndex, line.OffsetSpan, lineTypeStr);
+            }
+            sb.Append("\r\n");
+
+            if (!mProject.OperandFormats.TryGetValue(line.FileOffset, out FormatDescriptor dfd)) {
+                // No user-specified format, but there may be a generated format.
+                sb.AppendFormat(Res.Strings.INFO_FD_SUM_FMT, Res.Strings.DEFAULT_VALUE);
+                if (attr.DataDescriptor != null) {
+                    sb.Append(" [");
+                    sb.Append(attr.DataDescriptor.ToUiString());
+                    sb.Append("]");
+                }
+            } else {
+                // User-specified operand format.
+                // If the descriptor has a weak reference to an unknown symbol, should we
+                // call that out here?
+                sb.AppendFormat(Res.Strings.INFO_FD_SUM_FMT, dfd.ToUiString());
+            }
+            sb.Append("\r\n");
+
+            // Debug only
+            //sb.Append("DEBUG: opAddr=" + attr.OperandAddress.ToString("x4") +
+            //    " opOff=" + attr.OperandOffset.ToString("x4") + "\r\n");
+
+            sb.Append("\u2022Attributes:");
+            if (attr.IsHinted) {
+                sb.Append(" Hinted(");
+                for (int i = 0; i < line.OffsetSpan; i++) {
+                    switch (mProject.TypeHints[line.FileOffset + i]) {
+                        case CodeAnalysis.TypeHint.Code:
+                            sb.Append("C");
+                            break;
+                        case CodeAnalysis.TypeHint.Data:
+                            sb.Append("D");
+                            break;
+                        case CodeAnalysis.TypeHint.InlineData:
+                            sb.Append("I");
+                            break;
+                        default:
+                            break;
+                    }
+                    if (i > 8) {
+                        sb.Append("...");
+                        break;
+                    }
+                }
+                sb.Append(')');
+            }
+            if (attr.IsEntryPoint) {
+                sb.Append(" EntryPoint");
+            }
+            if (attr.IsBranchTarget) {
+                sb.Append(" BranchTarget");
+            }
+            if (attr.DoesNotContinue) {
+                sb.Append(" NoContinue");
+            }
+            if (attr.DoesNotBranch) {
+                sb.Append(" NoBranch");
+            }
+            if (mProject.StatusFlagOverrides[line.FileOffset].AsInt != 0) {
+                sb.Append(" StatusFlags");
+            }
+            sb.Append("\r\n\r\n");
+
+            if (attr.IsInstruction) {
+                Asm65.OpDef op = mProject.CpuDef.GetOpDef(mProject.FileData[line.FileOffset]);
+
+                string shortDesc = mOpDesc.GetShortDescription(op.Mnemonic);
+                if (!string.IsNullOrEmpty(shortDesc)) {
+                    if (op.IsUndocumented) {
+                        sb.Append("\u25b6[*] ");
+                    } else {
+                        sb.Append("\u25b6 ");
+                    }
+                    sb.Append(shortDesc);
+                    string addrStr = mOpDesc.GetAddressModeDescription(op.AddrMode);
+                    if (!string.IsNullOrEmpty(addrStr)) {
+                        sb.Append(", ");
+                        sb.Append(addrStr);
+                    }
+                    sb.Append("\r\n");
+                }
+
+                sb.Append("\u2022Cycles: ");
+                int cycles = op.Cycles;
+                Asm65.OpDef.CycleMod cycMods = op.CycleMods;
+                sb.Append(cycles.ToString());
+                if (cycMods != 0) {
+                    sb.Append(" (");
+                    int workBits = (int)cycMods;
+                    while (workBits != 0) {
+                        // Isolate rightmost bit.
+                        int firstBit = (~workBits + 1) & workBits;
+                        sb.Append(mOpDesc.GetCycleModDescription((OpDef.CycleMod)firstBit));
+                        // Remove from set.
+                        workBits &= ~firstBit;
+                        if (workBits != 0) {
+                            // more to come
+                            sb.Append(", ");
+                        }
+                    }
+                    sb.Append(")");
+                }
+                sb.Append("\r\n");
+
+                const string FLAGS = "NVMXDIZC";
+                sb.Append("\u2022Flags affected: ");
+                Asm65.StatusFlags affectedFlags = op.FlagsAffected;
+                for (int i = 0; i < 8; i++) {
+                    if (affectedFlags.GetBit((StatusFlags.FlagBits)(7 - i)) >= 0) {
+                        sb.Append(' ');
+                        sb.Append(FLAGS[i]);
+                    } else {
+                        sb.Append(" -");
+                    }
+                }
+                sb.Append("\r\n");
+
+                string longDesc = mOpDesc.GetLongDescription(op.Mnemonic);
+                if (!string.IsNullOrEmpty(longDesc)) {
+                    sb.Append("\r\n");
+                    sb.Append(longDesc);
+                    sb.Append("\r\n");
+                }
+            } else {
+                // do we want descriptions of the pseudo-ops?
+            }
+
+
+            // Publish
+            mMainWin.InfoBoxContents = sb.ToString();
+        }
+
+        #endregion Info panel
     }
 }
diff --git a/SourceGenWPF/ProjWin/MainWindow.xaml b/SourceGenWPF/ProjWin/MainWindow.xaml
index 1542f2d..8204c22 100644
--- a/SourceGenWPF/ProjWin/MainWindow.xaml
+++ b/SourceGenWPF/ProjWin/MainWindow.xaml
@@ -314,7 +314,9 @@ limitations under the License.
                 </GroupBox>
 
                 <GroupBox Grid.Row="2" Header="Info">
-                    <TextBox/>
+                    <TextBox Text="{Binding InfoBoxContents}"
+                             FontFamily="{StaticResource GeneralMonoFont}"
+                             TextWrapping="Wrap"/>
                 </GroupBox>
                 
                 <GridSplitter Height="4" Grid.Row="1"
diff --git a/SourceGenWPF/ProjWin/MainWindow.xaml.cs b/SourceGenWPF/ProjWin/MainWindow.xaml.cs
index 4a1816d..d922483 100644
--- a/SourceGenWPF/ProjWin/MainWindow.xaml.cs
+++ b/SourceGenWPF/ProjWin/MainWindow.xaml.cs
@@ -43,6 +43,11 @@ namespace SourceGenWPF.ProjWin {
         /// </summary>
         public DisplayList CodeDisplayList { get; private set; }
 
+        /// Version string, for display.
+        /// </summary>
+        public string ProgramVersionString {
+            get { return App.ProgramVersion.ToString(); }
+        }
 
         /// <summary>
         /// Reference to controller object.
@@ -203,11 +208,20 @@ namespace SourceGenWPF.ProjWin {
             get { return mShowCodeListView ? Visibility.Visible : Visibility.Hidden; }
         }
 
-        /// Version string, for display.
+        /// <summary>
+        /// Text to display in the Info panel.  This is a simple TextBox.
         /// </summary>
-        public string ProgramVersionString {
-            get { return App.ProgramVersion.ToString(); }
+        public string InfoBoxContents {
+            get {
+                return mInfoBoxContents;
+            }
+            set {
+                mInfoBoxContents = value;
+                OnPropertyChanged();
+            }
         }
+        private string mInfoBoxContents;
+
 
         private void CodeListView_SelectionChanged(object sender, SelectionChangedEventArgs e) {
             //DateTime startWhen = DateTime.Now;
@@ -215,8 +229,9 @@ namespace SourceGenWPF.ProjWin {
             // Update the selected-item bitmap.
             CodeDisplayList.SelectedIndices.SelectionChanged(e);
 
-            // Update the selection summary, which is used for can-execute methods.
-            mSelectionState = mMainCtrl.UpdateSelectionState();
+            // Notify MainController that the selection has changed.  This hands back an updated
+            // selection summary, which is used for "can execute" methods.
+            mMainCtrl.SelectionChanged(out mSelectionState);
 
             Debug.Assert(CodeDisplayList.SelectedIndices.DebugValidateSelectionCount(
                 codeListView.SelectedItems.Count));
diff --git a/SourceGenWPF/Res/Strings.xaml b/SourceGenWPF/Res/Strings.xaml
index 722af32..fd73346 100644
--- a/SourceGenWPF/Res/Strings.xaml
+++ b/SourceGenWPF/Res/Strings.xaml
@@ -3,6 +3,7 @@
                     xmlns:system="clr-namespace:System;assembly=mscorlib"
                     xmlns:local="clr-namespace:SourceGenWPF.Res">
 
+    <system:String x:Key="str_DefaultValue">Default</system:String>
     <system:String x:Key="str_ErrBadFd">Bad format descriptor at +{0:x6}.</system:String>
     <system:String x:Key="str_ErrBadFdFormat">Bad format descriptor type</system:String>
     <system:String x:Key="str_ErrBadFileLength">Bad file length</system:String>
@@ -27,6 +28,10 @@
     <system:String x:Key="str_FileFilterDis65">SourceGen projects(*.dis65)|*.dis65</system:String>
     <system:String x:Key="str_FileFilterSym65">SourceGen symbols (*.sym65)|*.sym65</system:String>
     <system:String x:Key="str_GeneratedForVersion">Target assembler: {0} v{1} [{2}]</system:String>
+    <system:String x:Key="str_InfoFdSumFmt">•Operand format is {0}</system:String>
+    <system:String x:Key="str_InfoLineSumNonFmt">Line {0}: {1}</system:String>
+    <system:String x:Key="str_InfoLineSumPluralFmt">Line {0}: {1} bytes of {2}</system:String>
+    <system:String x:Key="str_InfoLineSumSingularFmt">Line {0}: {1} byte of {2}</system:String>
     <system:String x:Key="str_InitialExtensionScripts">Extension scripts:</system:String>
     <system:String x:Key="str_InitialParameters">Default settings:</system:String>
     <system:String x:Key="str_InitialSymbolFiles">Symbol files:</system:String>
diff --git a/SourceGenWPF/Res/Strings.xaml.cs b/SourceGenWPF/Res/Strings.xaml.cs
index 616e32b..3379a1d 100644
--- a/SourceGenWPF/Res/Strings.xaml.cs
+++ b/SourceGenWPF/Res/Strings.xaml.cs
@@ -18,6 +18,8 @@ using System.Windows;
 
 namespace SourceGenWPF.Res {
     public static class Strings {
+        public static string DEFAULT_VALUE =
+            (string)Application.Current.FindResource("str_DefaultValue");
         public static string ERR_BAD_FD =
             (string)Application.Current.FindResource("str_ErrBadFd");
         public static string ERR_BAD_FD_FORMAT =
@@ -66,6 +68,14 @@ namespace SourceGenWPF.Res {
             (string)Application.Current.FindResource("str_FileFilterSym65");
         public static string GENERATED_FOR_VERSION_FMT =
             (string)Application.Current.FindResource("str_GeneratedForVersion");
+        public static string INFO_FD_SUM_FMT =
+            (string)Application.Current.FindResource("str_InfoFdSumFmt");
+        public static string INFO_LINE_SUM_NON_FMT =
+            (string)Application.Current.FindResource("str_InfoLineSumNonFmt");
+        public static string INFO_LINE_SUM_PLURAL_FMT =
+            (string)Application.Current.FindResource("str_InfoLineSumPluralFmt");
+        public static string INFO_LINE_SUM_SINGULAR_FMT =
+            (string)Application.Current.FindResource("str_InfoLineSumSingularFmt");
         public static string INITIAL_EXTENSION_SCRIPTS =
             (string)Application.Current.FindResource("str_InitialExtensionScripts");
         public static string INITIAL_PARAMETERS =