Drupal 8 is upon us and with it comes the Twigification of all theme output. Anything that was a PHP template or theme function in Drupal 7 is now a Twig template so we all need to level up on our Twiggy knowledge—and I'm not talking about this Twiggy or this Twiggy. 

Syntax

Printing 

{{ someVar }}

Comments

{# This is a comment, yo. #} 

Control Structures

{% if var %} 
... 
{% endif %}

{% for user in users if user.active %} 
	{{ user.name }} : {{ user.email }} 
{% else %} 
	{# No active users #}
{% endfor %}

Documentation

From the creators: 

• http://twig.sensiolabs.org/
• http://twig.sensiolabs.org/documentation
• http://twig.sensiolabs.org/doc/templates.html Good outline of syntax and semantics

Drupal specific:

• Twig theming overview: https://www.drupal.org/docs/8/theming/twig
• Working With Twig Templates: https://www.drupal.org/docs/8/theming/twig/working-with-twig-templates
• Twig Template naming conventions: https://www.drupal.org/docs/8/theming/twig/twig-template-naming-conventions
• Comparison of PHPTemplate and Twig theming paradigms: https://www.drupal.org/docs/8/theming/twig/comparison-of-phptemplate-and-twig-theming-paradigms
• Discovering and Inspecting Variables in Twig Templates: https://www.drupal.org/docs/8/theming/twig/discovering-and-inspecting-variables-in-twig-templates
• Debugging Twig templates: https://www.drupal.org/docs/8/theming/twig/debugging-twig-templates
• Debugging compiled Twig templates https://www.drupal.org/docs/8/theming/twig/debugging-compiled-twig-templates
• Locating Template Files with Debugging: https://www.drupal.org/docs/8/theming/twig/locating-template-files-with-debugging
• Filters - Modifying Variables In Twig Templates: https://www.drupal.org/docs/8/theming/twig/filters-modifying-variables-in-twig-templates
• Functions - In Twig Templates: https://www.drupal.org/docs/8/theming/twig/functions-in-twig-templates
• Macros in Twig Templates: https://www.drupal.org/docs/8/theming/twig/macros-in-twig-templates
• Twig best practices - preprocess functions and templates: https://www.drupal.org/docs/8/theming/twig/twig-best-practices-preprocess-functions-and-templates
• Create custom twig templates from custom module: https://www.drupal.org/docs/8/theming/twig/create-custom-twig-templates-from-custom-module 
• Drupal specific twig filters https://www.drupal.org/node/2357633

Tutorials:

• Not Drupal specific despite being on Drupalize.me but fairly comprehensive outline of all the concepts. 
  https://drupalize.me/videos/twig-basics?p=1899
  
  
• Overview page with links to all the Drupal-specific Twig videos.
  https://drupalize.me/tutorial/twig-drupal?p=2512

• Lots more in-depth and Drupal specific stuff here.
  https://drupalize.me/search?query=twig

Dev Setup

• Atom
  • Language support: https://github.com/reesef/php-twig
  • Snippets: https://gist.github.com/soniktrooth/593722ae72a57cd1a5d06efaa8a09ce8