diff --git a/components/fpspreadsheet/examples/other/chart/write_chart_demo.lpr b/components/fpspreadsheet/examples/other/chart/write_chart_demo.lpr
index f5990c884..5dc2a3749 100644
--- a/components/fpspreadsheet/examples/other/chart/write_chart_demo.lpr
+++ b/components/fpspreadsheet/examples/other/chart/write_chart_demo.lpr
@@ -73,6 +73,7 @@ begin
     ch.PlotArea.Background.Style := fsSolidFill;
     //ch.RotatedAxes := true;
     ch.StackMode := csmStackedPercentage;
+    //ch.Interpolation := ciCubicSpline;
 
     ch.XAxis.ShowLabels := true;
     ch.XAxis.LabelFont.Size := 9;
diff --git a/components/fpspreadsheet/laz_fpspreadsheet.lpk b/components/fpspreadsheet/laz_fpspreadsheet.lpk
index 97366824d..51533001b 100644
--- a/components/fpspreadsheet/laz_fpspreadsheet.lpk
+++ b/components/fpspreadsheet/laz_fpspreadsheet.lpk
@@ -33,7 +33,7 @@
 This package is all you need if you don't want graphical components (such as grids and charts)."/>
     <License Value="LGPL with static linking exception. This is the same license as is used in the LCL (Lazarus Component Library)."/>
     <Version Major="1" Minor="17"/>
-    <Files Count="59">
+    <Files Count="58">
       <Item1>
         <Filename Value="source\fps.inc"/>
         <Type Value="Include"/>
@@ -299,16 +299,12 @@ This package is all you need if you don&apos;t want graphical components (such a
       </Item56>
       <Item57>
         <Filename Value="source\common\fpschart.pas"/>
-        <UnitName Value="fpschart"/>
+        <UnitName Value="fpsChart"/>
       </Item57>
       <Item58>
         <Filename Value="source\common\fpspreadsheet_chart.inc"/>
         <Type Value="Binary"/>
       </Item58>
-      <Item59>
-        <Filename Value="source\common\fpschartstyles.pas"/>
-        <UnitName Value="fpschartstyles"/>
-      </Item59>
     </Files>
     <CompatibilityMode Value="True"/>
     <i18n>
diff --git a/components/fpspreadsheet/source/common/fpschart.pas b/components/fpspreadsheet/source/common/fpschart.pas
index 518e64f3a..c7cf1cb9a 100644
--- a/components/fpspreadsheet/source/common/fpschart.pas
+++ b/components/fpspreadsheet/source/common/fpschart.pas
@@ -198,7 +198,6 @@ type
     FLabelFormat: String;
     FLine: TsChartLine;
     FFill: TsChartFill;
-    FBorder: TsChartLine;
   public
     constructor Create(AChart: TsChart); virtual;
     destructor Destroy; override;
@@ -215,6 +214,7 @@ type
     function LabelsInCol: Boolean;
     function XValuesInCol: Boolean;
     function YValuesInCol: Boolean;
+
     property ChartType: TsChartType read FChartType;
     property Count: Integer read GetCount;
     property LabelFormat: String read FLabelFormat write FLabelFormat;  // Number format in Excel notation, e.g. '0.00'
@@ -224,7 +224,6 @@ type
     property YRange: TsCellRange read FYRange;
     property YAxis: TsChartAxisLink read FYAxis write FYAxis;
 
-    property Border: TsChartLine read FBorder write FBorder;
     property Fill: TsChartFill read FFill write FFill;
     property Line: TsChartLine read FLine write FLine;
   end;
@@ -250,18 +249,20 @@ type
     FSymbol: TsChartSeriesSymbol;
     FSymbolHeight: Double;  // in mm
     FSymbolWidth: Double;   // in mm
+    FShowLines: Boolean;
     FShowSymbols: Boolean;
-    function GetSymbolBorder: TsChartLine;
+    FBorder: TsChartLine;
     function GetSymbolFill: TsChartFill;
-    procedure SetSymbolBorder(Value: TsChartLine);
     procedure SetSymbolFill(Value: TsChartFill);
   public
     constructor Create(AChart: TsChart); override;
+    destructor Destroy; override;
     property Symbol: TsChartSeriesSymbol read FSymbol write FSymbol;
-    property SymbolBorder: TsChartLine read GetSymbolBorder write SetSymbolBorder;
+    property SymbolBorder: TsChartLine read FBorder write FBorder;
     property SymbolFill: TsChartFill read GetSymbolFill write SetSymbolFill;
     property SymbolHeight: double read FSymbolHeight write FSymbolHeight;
     property SymbolWidth: double read FSymbolWidth write FSymbolWidth;
+    property ShowLines: Boolean read FShowLines write FShowLines;
     property ShowSymbols: Boolean read FShowSymbols write FShowSymbols;
   end;
 
@@ -278,7 +279,12 @@ type
     property Items[AIndex: Integer]: TsChartSeries read GetItem write SetItem; default;
   end;
 
-  TsChartStackMode =(csmSideBySide, csmStacked, csmStackedPercentage);
+  TsChartStackMode = (csmSideBySide, csmStacked, csmStackedPercentage);
+  TsChartInterpolation = (
+    ciLinear,
+    ciCubicSpline, ciBSpline,
+    ciStepStart, ciStepEnd, ciStepCenterX, ciStepCenterY
+  );
 
   TsChart = class(TsChartFillElement)
   private
@@ -295,8 +301,9 @@ type
     FYAxis: TsChartAxis;
     FY2Axis: TsChartAxis;
 
-    FRotatedAxes: Boolean;   // For bar series: vertical columns <--> horizontal bars
-    FStackMode: TsChartStackMode;
+    FRotatedAxes: Boolean;        // For bar series: vertical columns <--> horizontal bars
+    FStackMode: TsChartStackMode; // For bar and area series
+    FInterpolation: TsChartInterpolation; // For line/scatter series: data connection lines
 
     FTitle: TsChartText;
     FSubTitle: TsChartText;
@@ -316,12 +323,7 @@ type
     function GetLineStyle(AIndex: Integer): TsChartLineStyle;
     function IsScatterChart: Boolean;
     function NumLineStyles: Integer;
-    {
-    function CategoriesInCol: Boolean;
-    function CategoriesInRow: Boolean;
-    function GetCategoryCount: Integer;
-    function HasCategories: Boolean;
-     }
+
     { Index of chart in workbook's chart list. }
     property Index: Integer read FIndex write FIndex;
     { Index of worksheet sheet which contains the chart. }
@@ -364,9 +366,11 @@ type
     { Attributes of the plot's secondary y axis (right) }
     property Y2Axis: TsChartAxis read FY2Axis write FY2Axis;
 
+    { Connecting line between data points (for line and scatter series) }
+    property Interpolation: TsChartInterpolation read FInterpolation write FInterpolation;
     { x and y axes exchanged (for bar series) }
     property RotatedAxes: Boolean read FRotatedAxes write FRotatedAxes;
-    { stacked series }
+    { Stacking of series (for bar and area series ) }
     property StackMode: TsChartStackMode read FStackMode write FStackMode;
 
     property CategoryLabelRange: TsCellRange read GetCategoryLabelRange;
@@ -573,11 +577,6 @@ begin
 
   idx := AChart.AddSeries(self);
 
-  FBorder := TsChartLine.Create;
-  FBorder.Style := clsSolid;
-  FBorder.Width := PtsToMM(DEFAULT_CHART_LINEWIDTH);
-  FBorder.Color := scBlack;
-
   FFill := TsChartFill.Create;
   FFill.Style := fsSolidFill;
   FFill.FgColor := DEFAULT_SERIES_COLORS[idx mod Length(DEFAULT_SERIES_COLORS)];
@@ -593,7 +592,6 @@ destructor TsChartSeries.Destroy;
 begin
   FLine.Free;
   FFill.Free;
-  FBorder.Free;
   inherited;
 end;
 
@@ -727,11 +725,19 @@ begin
   FChartType := ctLine;
   FSymbolWidth := 2.5;
   FSymbolHeight := 2.5;
+  FShowSymbols := false;
+  FShowLines := true;
+
+  FBorder := TsChartLine.Create;
+  FBorder.Style := clsSolid;
+  FBorder.Width := PtsToMM(DEFAULT_CHART_LINEWIDTH);
+  FBorder.Color := scBlack;
 end;
 
-function TsLineSeries.GetSymbolBorder: TsChartLine;
+destructor TsLineSeries.Destroy;
 begin
-  Result := FBorder;
+  FBorder.Free;
+  inherited;
 end;
 
 function TsLineSeries.GetSymbolFill: TsChartFill;
@@ -739,11 +745,6 @@ begin
   Result := FFill;
 end;
 
-procedure TsLineSeries.SetSymbolBorder(Value: TsChartLine);
-begin
-  FBorder := Value;
-end;
-
 procedure TsLineSeries.SetSymbolFill(Value: TsChartFill);
 begin
   FFill := Value;
diff --git a/components/fpspreadsheet/source/common/fpschartstyles.pas b/components/fpspreadsheet/source/common/fpschartstyles.pas
index 1d82096ad..9f140e256 100644
--- a/components/fpspreadsheet/source/common/fpschartstyles.pas
+++ b/components/fpspreadsheet/source/common/fpschartstyles.pas
@@ -336,7 +336,6 @@ begin
     ceX2AxisMinorGrid: Result := AChart.X2Axis.MinorGridLines;
     ceY2AxisMajorGrid: Result := AChart.Y2Axis.MajorGridLines;
     ceY2AxisMinorGrid: Result := AChart.Y2Axis.MinorGridLines;
-    ceSeriesBorder: Result := AChart.Series[AIndex].Border;
     ceSeriesLine: Result := AChart.Series[AIndex].Line;
     else
       raise Exception.Create('[TsChartLineRec.GetChartLine] Line not supported.');
diff --git a/components/fpspreadsheet/source/common/fpsopendocument.pas b/components/fpspreadsheet/source/common/fpsopendocument.pas
index 963d5bcf8..51598d5cd 100644
--- a/components/fpspreadsheet/source/common/fpsopendocument.pas
+++ b/components/fpspreadsheet/source/common/fpsopendocument.pas
@@ -7151,6 +7151,7 @@ begin
   series := AChart.Series[ASeriesIndex];
   sheet := TsWorkbook(FWorkbook).GetWorksheetByIndex(AChart.sheetIndex);
 
+  // These are the x values of a scatter plot.
   if series is TsScatterSeries then
   begin
     domainRange := GetSheetCellRangeString_ODS(
@@ -7161,12 +7162,15 @@ begin
     );
   end;
 
+  // These are the y values
   valuesRange := GetSheetCellRangeString_ODS(
     sheet.Name, sheet.Name,
     series.YRange.Row1, series.YRange.Col1,
     series.YRange.Row2, series.YRange.Col2,
     rfAllRel, false
   );
+
+  // And these are the data point labels.
   titleAddr := GetSheetCellRangeString_ODS(
     sheet.Name, sheet.Name,
     series.TitleAddr.Row, series.TitleAddr.Col,
@@ -7174,7 +7178,7 @@ begin
     rfAllRel, false);
   count := series.YRange.Row2 - series.YRange.Row1 + 1;
 
-  // Series properties
+  // Store the series properties
   AppendToStream(AChartStream, Format(
     indent + '<chart:series chart:style-name="ch%d" ' +
                'chart:values-cell-range-address="%s" ' +      // y values
@@ -7448,6 +7452,7 @@ function TsSpreadOpenDocWriter.GetChartPlotAreaStyleAsXML(AChart: TsChart;
   AIndent, AStyleID: Integer): String;
 var
   indent: String;
+  interpolationStr: String = '';
   verticalStr: String = '';
   stackModeStr: String = '';
 begin
@@ -7455,15 +7460,27 @@ begin
 
   if AChart.RotatedAxes then
     verticalStr := 'chart:vertical="true" ';
+
   case AChart.StackMode of
     csmSideBySide: ;
     csmStacked: stackModeStr := 'chart:stacked="true" ';
     csmStackedPercentage: stackModeStr := 'chart:percentage="true" ';
   end;
 
+  case AChart.Interpolation of
+    ciLinear: ;
+    ciCubicSpline: interpolationStr := 'chart:interpolation="cubic-spline" ';
+    ciBSpline: interpolationStr := 'chart:interpolation="b-spline" ';
+    ciStepStart: interpolationStr := 'chart:interpolation="step-start" ';
+    ciStepEnd: interpolationStr := 'chart:interpolation="step-end" ';
+    ciStepCenterX: interpolationStr := 'chart:interpolation="step-center-x" ';
+    ciStepCenterY: interpolationStr := 'chart:interpolation="step-center-y" ';
+  end;
+
   Result := Format(
     indent + '  <style:style style:name="ch%d" style:family="chart">' + LE +
     indent + '    <style:chart-properties ' +
+                   interpolationStr +
                    verticalStr +
                    stackModeStr +
                    'chart:symbol-type="automatic" ' +
@@ -7502,13 +7519,13 @@ var
   textProps: String = '';
   lineProps: String = '';
   fillProps: String = '';
-  s: String;
 begin
   Result := '';
 
   indent := DupeString(' ', AIndent);
   series := AChart.Series[ASeriesIndex];
 
+  // Chart properties
   chartProps := 'chart:symbol-type="none" ';
   if (series is TsLineSeries) then
   begin
@@ -7522,16 +7539,19 @@ begin
   end;
   chartProps := chartProps + 'chart:link-data-style-to-source="true" ';
 
+  // Graphic properties
   lineProps := GetChartLineStyleGraphicPropsAsXML(AChart, series.Line);
   fillProps := GetChartFillStyleGraphicPropsAsXML(AChart, series.Fill);
-  if (lineser <> nil) then
+  if (series is TsLineSeries) then
   begin
-    if (lineSer.ShowSymbols) then
-      graphProps := lineProps + fillProps
-    else
-      graphProps := lineProps;
-  end;
+    if lineSer.ShowSymbols then
+      graphProps := graphProps + fillProps;
+    if lineSer.ShowLines and (lineser.Line.Style <> clsNoLine) then
+      graphProps := graphProps + lineProps;
+  end else
+    graphProps := fillProps + lineProps;
 
+  // Text properties
   textProps := 'fo:font-size="10pt" style:font-size-asian="10pt" style:font-size-complex="10pt" ';
 //  textProps := WriteFontStyleXMLAsString(font);    // <--- to be completed. this is for the series labels.