router-outlet is not a known element
<p>The following code works:</p>

<pre><code>/*app.module.ts*/
import { NgModule } from '@angular/core';
import { HttpModule } from '@angular/http';
import { AppComponent } from './app.component';
import { LetterRecall } from './letterRecall/letterRecall.component';

@NgModule({
    imports:      [BrowserModule, HttpModule],
    declarations: [AppComponent, LetterRecall],
    bootstrap:    [AppComponent],
})
export class AppModule {}

/*app.component.ts*/
import {Component} from '@angular/core';
@Component({
    selector: 'my-app',
    templateUrl: 'app/app.component.html'
})
export class AppComponent { }

/*app.component.html*/
&lt;h3&gt;Title&lt;/h3&gt;
&lt;letter-recall&gt;&lt;/letter-recall&gt;
</code></pre>

<hr>

<p>Following the Angular Routing Tutorial here: <a href="https://angular.io/docs/ts/latest/tutorial/toh-pt5.html" rel="noreferrer">https://angular.io/docs/ts/latest/tutorial/toh-pt5.html</a></p>

<p>I modified my code to:</p>

<pre><code>/*index.html*/
&lt;head&gt;
   &lt;base href="/"&gt;

/*app.module.ts*/
import { NgModule } from '@angular/core';
import { HttpModule } from '@angular/http';
import { RouterModule } from '@angular/router';
import { AppComponent } from './app.component';
import { LetterRecall } from './letterRecall/letterRecall.component';

@NgModule({
    imports:      [BrowserModule, 
                   HttpModule,
                   RouterModule.forRoot([
                       { path: 'letters', component: LetterRecall }
                   ])],
    declarations: [AppComponent, LetterRecall],
    bootstrap:    [AppComponent],
})
export class AppModule {}

/*app.component.ts*/
import {Component} from '@angular/core';
@Component({
    selector: 'my-app',
    templateUrl: 'app/app.component.html'
})
export class AppComponent { }

/*app.component.html*/
&lt;h3&gt;Title&lt;/h3&gt;
&lt;a routerLink="/letters"&gt;Letters&lt;/a&gt;
&lt;router-outlet&gt;&lt;/router-outlet&gt;
</code></pre>

<p>At this point I get the following error: </p>

<blockquote>
  <p>"Unhandled Promise rejection: Template parse errors: 'router-outlet'
  is not a known element:
  1. If 'router-outlet' is an Angular component, then verify that it is part of this module. ....."</p>
</blockquote>

<p>I am using the following versions:</p>

<pre><code>    "@angular/common": "2.4.0",
    "@angular/compiler": "2.4.0",
    "@angular/core": "2.4.0",
    "@angular/forms": "2.4.0",
    "@angular/http": "2.4.0",
    "@angular/platform-browser": "2.4.0",
    "@angular/platform-browser-dynamic": "2.4.0",
    "@angular/router": "3.4.0"
</code></pre>

<hr>

<p>All of the other answers on SO indicate I need to import RouterModule but as you can see above, I am doing this as prescribed in the tutorial. </p>

<p>Any suggestions on where I can look for the source of this error? I started off using John Papa's First Look tutorial on PluralSight but it looks like that code is a little old now. That's when I stripped all of that out and went bare-bones through the tutorial and I get this error... I am not sure where to turn next. </p>