Add a ColumnDefinition to Grid
<Window xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" x:Class="columndefinitions_grid.Window1" Title="ColumnDefinitions Sample"> <Border BorderBrush="Black" Background="White" BorderThickness="2"> <DockPanel Margin="10,0,0,0"> <TextBlock FontSize="20" FontWeight="Bold" DockPanel.Dock="Top">Grid Column and Row Collections</TextBlock> <Grid DockPanel.Dock="Top" HorizontalAlignment="Left" Name="grid1" ShowGridLines="true" Width="625" Height="400"> <Grid.ColumnDefinitions> <ColumnDefinition/> <ColumnDefinition/> <ColumnDefinition/> </Grid.ColumnDefinitions> <Grid.RowDefinitions> <RowDefinition/> <RowDefinition/> <RowDefinition/> </Grid.RowDefinitions> </Grid> <StackPanel HorizontalAlignment="Left" Orientation="Horizontal" Width="625" DockPanel.Dock="Top"> <Button Width="125" Click="addCol">Add Column</Button> </StackPanel> </DockPanel> </Border> </Window> //File:Window.xaml.vb Imports System Imports System.Windows Imports System.Windows.Controls Imports System.Windows.Documents Namespace columndefinitions_grid Public Partial Class Window1 Inherits Window Private rowDef1 As RowDefinition Private colDef1 As ColumnDefinition Private Sub addCol(sender As Object, e As RoutedEventArgs) colDef1 = New ColumnDefinition() grid1.ColumnDefinitions.Add(colDef1) End Sub End Class End Namespace