How do I share data between components in Angular 2?

A service singleton is a nice solution. Other way - data/events bindings.

Here is an example of both:

class BazService{
  n: number = 0;
  inc(){
    this.n++;
  }
}

@Component({
  selector: 'foo'
})
@View({
  template: `<button (click)="foobaz.inc()">Foo {{ foobaz.n }}</button>`
})
class FooComponent{
  constructor(foobaz: BazService){
    this.foobaz = foobaz;
  }
}

@Component({
  selector: 'bar',
  properties: ['prop']
})
@View({
  template: `<button (click)="barbaz.inc()">Bar {{ barbaz.n }}, Foo {{ prop.foobaz.n }}</button>`
})
class BarComponent{
  constructor(barbaz: BazService){
    this.barbaz = barbaz;
  }
}

@Component({
    selector: 'app',
    viewInjector: [BazService]
})
@View({
  template: `
    <foo #f></foo>
    <bar [prop]="f"></bar>
  `,
  directives: [FooComponent, BarComponent]
})
class AppComponent{}

bootstrap(AppComponent);

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The comment by @maufarinelli deserves its own answer because until I saw it, I was still bashing my head against the wall with this issue even with @Alexander Ermolov's answer.

The problem is that when you add a providers to your component:

@Component({
    selector: 'my-selector',
    providers: [MyService],
    template: `<div>stuff</div>`
})

This causes a new instance of your service to be injected... rather than being a singleton.

So remove all instances of your providers: [MyService] in your application except in the module, and it will work!