Sorting posts on category page – I need a little extra code

This is my basic loop for a category page where I’m inserting links to each post with an excerpt acting as a description.

What do I need to do to sort the posts alphabetically?

<?php foreach ($posts as $post) : start_wp(); ?>
<div class=”post”>

<h2 class=”post-title”>“> <?php the_title(); ?> </h2>

<div class=”post-content”>
<?php the_excerpt(); ?>
</div>
</div>

<?php endforeach; ?>