Thank you for your help, Elizabeth. I believe that this is probably the answer I need, but I'm having difficulty translating it from VB. Are you able to help me with that? Thanks again!

Hello again,

When I attempt to implement this code verbatim, I see no change in my chart gridlines. The only change I had to make was converting the igChart reference to igWebChart in the xaml. If you have any insight into why this might be the case, I would greatly appreciate it. Thanks again!

I'm sorry, I should probably be more clear - my gridlines don't appear dotted no matter what I try with this approach. The xamChart to xamWebChart is just the only modification I made after copying and pasting. I receive no errors, and the gridlines just display as normal.

Thank you Graham! I'm not sure what the difference was between your code and mine, but everything works now.

Hmm... works for me...

Are you sure you are assigning the grid line style?

                    <igChart:Axis.MajorGridline>
                        <igChart:GridlineGroup Stroke="Red" StrokeThickness="3" GridlineStyle="{StaticResource LineStyle}" />
                    </igChart:Axis.MajorGridline>

Here is the full code of my sample in c#:

The xaml:

<UserControl x:Class="SilverlightApplication109.MainPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
    xmlns:igChart="clr-namespace:Infragistics.Silverlight.Chart;assembly=InfragisticsSL4.Controls.Charts.XamWebChart.v10.3" 
    xmlns:local="clr-namespace:SilverlightApplication109" mc:Ignorable="d"
    d:DesignHeight="300" d:DesignWidth="400">
    <UserControl.Resources>
        <Style x:Key="LineStyle" TargetType="igChart:Mark">
            <Setter Property="StrokeThickness" Value=".5"/>
            <Setter Property="Stroke" Value="#FFE6EFF7"/>
            <Setter Property="Fill" Value="#FFE6EFF7"/>
            <Setter Property="Template">
                <Setter.Value>
                    <ControlTemplate TargetType="igChart:Mark">
                        <Grid x:Name="parentGrid">
                            <Grid.Resources>
                                <local:DoublingConverter x:Key="DoublingConverter"/>
                            </Grid.Resources>
                            <local:BoundsRectangle x:Name="Bounds" />

                            <Path UseLayoutRounding="True" Stroke="{TemplateBinding Stroke}" 
                                  StrokeThickness="{Binding Path=StrokeThickness, RelativeSource={RelativeSource TemplatedParent}, Converter={StaticResource DoublingConverter}}"
                                  StrokeDashArray="3" 
                                  Data="{Binding ElementName=Bounds, Path=PathData, Mode=OneWay}">
                            </Path>
                        </Grid>
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>
    </UserControl.Resources>

    <Grid x:Name="LayoutRoot">
        <igChart:XamWebChart>
            <igChart:XamWebChart.Axes>
                <igChart:Axis AxisType="PrimaryY">
                    <igChart:Axis.MajorGridline>
                        <igChart:GridlineGroup Stroke="Red" StrokeThickness="3" GridlineStyle="{StaticResource LineStyle}" />
                    </igChart:Axis.MajorGridline>
                </igChart:Axis>
            </igChart:XamWebChart.Axes>

            <igChart:XamWebChart.Series>
                <igChart:Series>
                    <igChart:Series.DataPoints>
                        <igChart:DataPoint Value="1" />
                        <igChart:DataPoint Value="2" />
                        <igChart:DataPoint Value="3" />
                        <igChart:DataPoint Value="4" />
                        <igChart:DataPoint Value="5" />
                    </igChart:Series.DataPoints>
                </igChart:Series>
            </igChart:XamWebChart.Series>
        </igChart:XamWebChart>
    </Grid>

</UserControl>

And the code behind:

using System;
using System.Collections;
using System.Collections.Generic;
using System.Diagnostics;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Media;

namespace SilverlightApplication109
{

    public partial class MainPage : UserControl
    {
        public MainPage()
        {
            InitializeComponent();
        }
    }


    public class BoundsRectangle : Panel
    {
        public static DependencyProperty PathDataProperty =
        DependencyProperty.Register(
        "PathData",
        typeof(GeometryGroup),
        typeof(BoundsRectangle),
        new PropertyMetadata(PathDataPropertyChanged));

        public BoundsRectangle()
        {
            this.SizeChanged += OnSizeChanged;
        }

        public GeometryGroup PathData
        {
            get { return (GeometryGroup)GetValue(PathDataProperty); }
            set { SetValue(PathDataProperty, value); }
        }


        private void OnSizeChanged(
            object sender,
            SizeChangedEventArgs args)
        {
            double newWidth = args.NewSize.Width;

            GeometryGroup newData = new GeometryGroup();
            LineGeometry top = new LineGeometry();
            top.StartPoint = new Point(0, 0);
            top.EndPoint = new Point(newWidth, 0);

            newData.Children.Add(top);

            PathData = newData;
        }

        private static void PathDataPropertyChanged(
            DependencyObject sender,
        DependencyPropertyChangedEventArgs args)
        {
        }
    }

    public class DoublingConverter : IValueConverter
    {
        public object Convert(
            object value,
            Type targetType,
            object parameter,
            System.Globalization.CultureInfo culture)
        {
            if (value != null && value is double)
            {
                return (double)value * 2.0;
            }

            return null;
        }

        public object ConvertBack(
            object value, 
            Type targetType, 
            object parameter,
        System.Globalization.CultureInfo culture)
        {
            throw new NotImplementedException();
        }
    }
}

-Graham