The right way to do this is to prevent the form from getting visible in the first place. That requires overriding SetVisibleCore(). Let s assume a context menu for the NotifyIcon with a Show and Exit command. You can implement it like this:

public partial class Form1 : Form {
    public Form1() {
        InitializeComponent();
        notifyIcon1.ContextMenuStrip = contextMenuStrip1;
        this.showToolStripMenuItem.Click += showToolStripMenuItem_Click;
        this.exitToolStripMenuItem.Click += exitToolStripMenuItem_Click;
    }

    private bool allowVisible;     // ContextMenu s Show command used
    private bool allowClose;       // ContextMenu s Exit command used

    protected override void SetVisibleCore(bool value) {
        if (!allowVisible) {
            value = false;
            if (!this.IsHandleCreated) CreateHandle();
        }
        base.SetVisibleCore(value);
    }

    protected override void OnFormClosing(FormClosingEventArgs e) {
        if (!allowClose) {
            this.Hide();
            e.Cancel = true;
        }
        base.OnFormClosing(e);
    }

    private void showToolStripMenuItem_Click(object sender, EventArgs e) {
        allowVisible = true;
        Show();
    }

    private void exitToolStripMenuItem_Click(object sender, EventArgs e) {
        allowClose = true;
        Application.Exit();
    }
}

Note a wrinkle with the Load event, it won t fire until the main form is first shown. So be sure to do initialization in the form s constructor, not the Load event handler.

I m reading all the answers and see hacks and black magic... (no offense, mates)

No hacks needed. You don t even have to set "ShowInTaskbar=false" and other stuff. Just do this:

    //"Form Shown" event handler
    private void Form_Shown(object sender, EventArgs e)
    {
        //to minimize window
        this.WindowState = FormWindowState.Minimized;

        //to hide from taskbar
        this.Hide();
    }

NOTE: I strongly recommend NOT TOUCHING the "ShowInTaskbar" property. For example, if your application registers system-wide hotkeys or other similar stuff (hooks, etc) - setting ShowInTaskBar=false and minimizing your app will prevent Windows from sending some messages to your window... And your hooks/hotkeys/etc will stop working.

In the constructor, remove these two lines:

this.Visible = false;
this.ShowInTaskbar = false;

and add after InitializeComponent();:

this.WindowState = FormWindowState.Minimized;

In designer, set ShowInTaskbar to false & FormWindowState to Normal.

EDIT: If you post the same in Load event, the window does get minimized but still shows minimized on the desktop. I think this is a bug.

When minimizing an application and you want to hide it from Alt+Tab:

You also need to set the Opacity to stop the titlebar showing near the Start Menu when you set the Border Style to a Tool Window.

On Minimize Event:

this.Visible = false;
this.Opacity = 0;
this.FormBorderStyle = FormBorderStyle.FixedToolWindow;
this.ShowInTaskbar = false;

On Normalize Event:

this.Visible = true;
this.Opacity = 100;
this.FormBorderStyle = FormBorderStyle.FixedSingle; //or whatever it was previously set to
this.ShowInTaskbar = true;

Move the following code from the Form s constructor to Form_Main_Load(). With the same setup on Notification_Icon when Form_Resize().

// Hide the Form to System Tray
this.WindowState = FormWindowState.Minimized;

This "quick and dirty fix" worked for me:

$form1.FormBorderStyle = "fixedtoolwindow"
$form1.top = -1000000
$form1.Left = -1000000
$form1.Width = 10
$form1.Height = 10
$form1.WindowState = "normal"
$form1.ShowInTaskbar = $False
$form1.Opacity = 0
$form1.Hide()

Hope it helps someone else...