Dim dlg As New OpenFileDialog()

' Show all files
dlg.Filter = String.Empty

dlg.ShowDialog()

Dim dlg As New OpenFileDialog()

' Show all files
dlg.Filter = Nothing

dlg.ShowDialog()

Dim dlg As New OpenFileDialog()

' Filter by Word Documents
dlg.Filter = "Word Documents|*.doc"

dlg.ShowDialog()

Dim dlg As New OpenFileDialog()

' Filter by Excel Worksheets
dlg.Filter = "Excel Worksheets|*.xls"

dlg.ShowDialog()

Dim dlg As New OpenFileDialog()

' Filter by PowerPoint Presentations
dlg.Filter = "PowerPoint Presentations|*.ppt"

dlg.ShowDialog()

Dim dlg As New OpenFileDialog()

' Filter by Office Files
dlg.Filter = "Office Files|*.doc;*.xls;*.ppt"

dlg.ShowDialog()

Dim dlg As New OpenFileDialog()

' Filter by All Files
dlg.Filter = "All Files|*.*"

dlg.ShowDialog()

Dim dlg As New OpenFileDialog()

' Filter by Word Documents OR Excel Worksheets OR PowerPoint Presentations 
'           OR Office Files 
'           OR All Files
dlg.Filter = "Word Documents|*.doc|Excel Worksheets|*.xls|PowerPoint Presentations|*.ppt" & "|Office Files|*.doc;*.xls;*.ppt" & "|All Files|*.*"

dlg.ShowDialog()