Twitter Bootstrap multiple accordions but only one open panel at a time

The accepted answer is good, but doesn't exactly answer what they did in order to make that work.

In this fiddle you can see the bare-minimum code that's needed, which is:

 <div class="panel-group" id="panels">
    <div class="panel panel-default">
        <div class="collapsed" data-toggle="collapse" data-parent="#panels" data-target="#firstPanel">
             <h4>First header</h4>    
        </div>
        <div id="firstPanel" class="panel-collapse collapse">
            <div>Content.</div>
        </div>
    </div>
    <div class="panel panel-default">
        <div class="collapsed" data-toggle="collapse" data-parent="#panels" data-target="#secondPanel">
             <h4>Second header</h4>

        </div>
        <div id="secondPanel" class="panel-collapse collapse">
            <div>Other content.</div>
        </div>
    </div>
</div>

Notice that each panel has a data-parent which targets the parent div with the ID #panels.

That is the magic sauce you need.

Try this:

  <div class="panel-group" id="accordion1">
    <div class="panel panel-default">
        <div class="panel-heading accordion-toggle collapsed" data-toggle="collapse" data-parent="#accordion1,#accordion2,#accordion3" data-target="#collapseOne1">
             <h4 class="panel-title">Collapsible Group Item #1</h4>

        </div>
        <div id="collapseOne1" class="panel-collapse collapse">
            <div class="panel-body">Anim pariatur cliche reprehenderit, enim eiusmod high life accusamus terry richardson ad squid. 3 wolf moon officia aute, non cupidatat skateboard dolor brunch. Food truck quinoa nesciunt laborum eiusmod. Brunch 3 wolf moon tempor, sunt aliqua put a bird on it squid single-origin coffee nulla assumenda shoreditch et. Nihil anim keffiyeh helvetica, craft beer labore wes anderson cred nesciunt sapiente ea proident. Ad vegan excepteur butcher vice lomo. Leggings occaecat craft beer farm-to-table, raw denim aesthetic synth nesciunt you probably haven't heard of them accusamus labore sustainable VHS.</div>
        </div>
    </div>
    <div class="panel panel-default">
        <div class="panel-heading accordion-toggle collapsed" data-toggle="collapse" data-parent="#accordion1,#accordion2,#accordion3" data-target="#collapseTwo1">
             <h4 class="panel-title">Collapsible Group Item #2</h4>

        </div>
        <div id="collapseTwo1" class="panel-collapse collapse">
            <div class="panel-body">Anim pariatur cliche reprehenderit, enim eiusmod high life accusamus terry richardson ad squid. 3 wolf moon officia aute, non cupidatat skateboard dolor brunch. Food truck quinoa nesciunt laborum eiusmod. Brunch 3 wolf moon tempor, sunt aliqua put a bird on it squid single-origin coffee nulla assumenda shoreditch et. Nihil anim keffiyeh helvetica, craft beer labore wes anderson cred nesciunt sapiente ea proident. Ad vegan excepteur butcher vice lomo. Leggings occaecat craft beer farm-to-table, raw denim aesthetic synth nesciunt you probably haven't heard of them accusamus labore sustainable VHS.</div>
        </div>
    </div>
    <div class="panel panel-default">
        <div class="panel-heading accordion-toggle collapsed" data-toggle="collapse" data-parent="#accordion1,#accordion2,#accordion3" data-target="#collapseThree1">
             <h4 class="panel-title">Collapsible Group Item #3</h4>

        </div>
        <div id="collapseThree1" class="panel-collapse collapse">
            <div class="panel-body">Anim pariatur cliche reprehenderit, enim eiusmod high life accusamus terry richardson ad squid. 3 wolf moon officia aute, non cupidatat skateboard dolor brunch. Food truck quinoa nesciunt laborum eiusmod. Brunch 3 wolf moon tempor, sunt aliqua put a bird on it squid single-origin coffee nulla assumenda shoreditch et. Nihil anim keffiyeh helvetica, craft beer labore wes anderson cred nesciunt sapiente ea proident. Ad vegan excepteur butcher vice lomo. Leggings occaecat craft beer farm-to-table, raw denim aesthetic synth nesciunt you probably haven't heard of them accusamus labore sustainable VHS.</div>
        </div>
    </div>
</div>
<div class="panel-group" id="accordion2">
    <div class="panel panel-default">
        <div class="panel-heading accordion-toggle collapsed" data-toggle="collapse" data-parent="#accordion1,#accordion2,#accordion3" data-target="#collapseOne2">
             <h4 class="panel-title">Collapsible Group Item #1</h4>

        </div>
        <div id="collapseOne2" class="panel-collapse collapse">
            <div class="panel-body">Anim pariatur cliche reprehenderit, enim eiusmod high life accusamus terry richardson ad squid. 3 wolf moon officia aute, non cupidatat skateboard dolor brunch. Food truck quinoa nesciunt laborum eiusmod. Brunch 3 wolf moon tempor, sunt aliqua put a bird on it squid single-origin coffee nulla assumenda shoreditch et. Nihil anim keffiyeh helvetica, craft beer labore wes anderson cred nesciunt sapiente ea proident. Ad vegan excepteur butcher vice lomo. Leggings occaecat craft beer farm-to-table, raw denim aesthetic synth nesciunt you probably haven't heard of them accusamus labore sustainable VHS.</div>
        </div>
    </div>
    <div class="panel panel-default">
        <div class="panel-heading accordion-toggle collapsed" data-toggle="collapse" data-parent="#accordion1,#accordion2,#accordion3" data-target="#collapseTwo2">
             <h4 class="panel-title">Collapsible Group Item #2</h4>

        </div>
        <div id="collapseTwo2" class="panel-collapse collapse">
            <div class="panel-body">Anim pariatur cliche reprehenderit, enim eiusmod high life accusamus terry richardson ad squid. 3 wolf moon officia aute, non cupidatat skateboard dolor brunch. Food truck quinoa nesciunt laborum eiusmod. Brunch 3 wolf moon tempor, sunt aliqua put a bird on it squid single-origin coffee nulla assumenda shoreditch et. Nihil anim keffiyeh helvetica, craft beer labore wes anderson cred nesciunt sapiente ea proident. Ad vegan excepteur butcher vice lomo. Leggings occaecat craft beer farm-to-table, raw denim aesthetic synth nesciunt you probably haven't heard of them accusamus labore sustainable VHS.</div>
        </div>
    </div>
    <div class="panel panel-default">
        <div class="panel-heading accordion-toggle collapsed" data-toggle="collapse" data-parent="#accordion1,#accordion2,#accordion3" data-target="#collapseThree2">
             <h4 class="panel-title">Collapsible Group Item #3</h4>

        </div>
        <div id="collapseThree2" class="panel-collapse collapse">
            <div class="panel-body">Anim pariatur cliche reprehenderit, enim eiusmod high life accusamus terry richardson ad squid. 3 wolf moon officia aute, non cupidatat skateboard dolor brunch. Food truck quinoa nesciunt laborum eiusmod. Brunch 3 wolf moon tempor, sunt aliqua put a bird on it squid single-origin coffee nulla assumenda shoreditch et. Nihil anim keffiyeh helvetica, craft beer labore wes anderson cred nesciunt sapiente ea proident. Ad vegan excepteur butcher vice lomo. Leggings occaecat craft beer farm-to-table, raw denim aesthetic synth nesciunt you probably haven't heard of them accusamus labore sustainable VHS.</div>
        </div>
    </div>
</div>
<div class="panel-group" id="accordion3">
    <div class="panel panel-default">
        <div class="panel-heading accordion-toggle collapsed" data-toggle="collapse" data-parent="#accordion1,#accordion2,#accordion3" data-target="#collapseOne3">
             <h4 class="panel-title">Collapsible Group Item #1</h4>

        </div>
        <div id="collapseOne3" class="panel-collapse collapse">
            <div class="panel-body">Anim pariatur cliche reprehenderit, enim eiusmod high life accusamus terry richardson ad squid. 3 wolf moon officia aute, non cupidatat skateboard dolor brunch. Food truck quinoa nesciunt laborum eiusmod. Brunch 3 wolf moon tempor, sunt aliqua put a bird on it squid single-origin coffee nulla assumenda shoreditch et. Nihil anim keffiyeh helvetica, craft beer labore wes anderson cred nesciunt sapiente ea proident. Ad vegan excepteur butcher vice lomo. Leggings occaecat craft beer farm-to-table, raw denim aesthetic synth nesciunt you probably haven't heard of them accusamus labore sustainable VHS.</div>
        </div>
    </div>
    <div class="panel panel-default">
        <div class="panel-heading accordion-toggle collapsed" data-toggle="collapse" data-parent="#accordion1,#accordion2,#accordion3" data-target="#collapseTwo3">
             <h4 class="panel-title">Collapsible Group Item #2</h4>

        </div>
        <div id="collapseTwo3" class="panel-collapse collapse">
            <div class="panel-body">Anim pariatur cliche reprehenderit, enim eiusmod high life accusamus terry richardson ad squid. 3 wolf moon officia aute, non cupidatat skateboard dolor brunch. Food truck quinoa nesciunt laborum eiusmod. Brunch 3 wolf moon tempor, sunt aliqua put a bird on it squid single-origin coffee nulla assumenda shoreditch et. Nihil anim keffiyeh helvetica, craft beer labore wes anderson cred nesciunt sapiente ea proident. Ad vegan excepteur butcher vice lomo. Leggings occaecat craft beer farm-to-table, raw denim aesthetic synth nesciunt you probably haven't heard of them accusamus labore sustainable VHS.</div>
        </div>
    </div>
    <div class="panel panel-default">
        <div class="panel-heading accordion-toggle collapsed" data-toggle="collapse" data-parent="#accordion1,#accordion2,#accordion3" data-target="#collapseThree3">
             <h4 class="panel-title">Collapsible Group Item #3</h4>

        </div>
        <div id="collapseThree3" class="panel-collapse collapse">
            <div class="panel-body">Anim pariatur cliche reprehenderit, enim eiusmod high life accusamus terry richardson ad squid. 3 wolf moon officia aute, non cupidatat skateboard dolor brunch. Food truck quinoa nesciunt laborum eiusmod. Brunch 3 wolf moon tempor, sunt aliqua put a bird on it squid single-origin coffee nulla assumenda shoreditch et. Nihil anim keffiyeh helvetica, craft beer labore wes anderson cred nesciunt sapiente ea proident. Ad vegan excepteur butcher vice lomo. Leggings occaecat craft beer farm-to-table, raw denim aesthetic synth nesciunt you probably haven't heard of them accusamus labore sustainable VHS.</div>
        </div>
    </div>
</div>

Add this javascript:

$('.collapse').on('show.bs.collapse', function () {
    $otherPanels = $(this).parents('.panel-group').siblings('.panel-group');
    $('.collapse',$otherPanels).removeClass('in');
});