Next and Previous Nodes

page.tpl.php

<?php if($next_node): ?>
<a href="node/<?php print $next_node; ?>">Next Node</a>
<?php endif; ?>

template.php

function hook_preprocess_page(&$variables, $hook) {
  if(arg(0) == 'node' && is_numeric(arg(1)) && $node = node_load(arg(1)) {
    if($node->type == 'case_study') {
      $query = new EntityFieldQuery();
      $entities = $query->entityCondition('entity_type', 'node')
                        ->entityCondition('bundle', 'case_study')
                        ->propertyCondition('status', 1)
                        ->propertyOrderBy('nid', 'ASC')
                        ->execute();

      $nodes = node_load_multiple(array_keys($entities['node']));
      if(count($nodes) > 0) {
        $next_node = reset($nodes);
      }
              
      $variables['current_node'] = $node->nid;
      $variables['next_node'] = $next_node->nid;
      $variables['prev_node'] = $node->nid - 1;
    }
  }
}