you got one option...PHP ...all WP plugins are written in PHP...and knowing javascript / HTML will help greatly too depending on what your plugin does and how it interfaces with the user

FYI: i would start here: http://codex.wordpress.org/Writing_a_Plugin

Strong PHP knowledge is a required minimum. You will also need to learn the basics of MySQL and JavaScript.

Nope, there is no something which I can recommend to you, because I have no idea about your background. Are you familiar with programming in general? I.e. do you understand that algorithms are etc? Do you know any other programming languages like C/C++ etc? If you don't, it will be a very stupid idea to start with any PHP book/course right now, since you must to learn the common programming basics first.

Find some tutorial sites to get started. Creating wordpress plugins does require some fairly advanced knowledge of how PHP and how Wordpress works, and I don't think you have either.

Spend a few months learning how to create basic PHP programs, find tutorial websites and learn to love PHP: Hypertext Preprocessor

<?php echo 'PHP Rocks... '; ?>

I learned PHP from w3schools.com

I'm not sure how much you know about programming or web developing, so:

Just in case you don't know - you should learn HTML first.
HTML is very easy.

Then move on to the basics of javascript . It is not required, but i strongly recommend you to learn it. Maybe even learn some javascript library (jQuery is my favourite).

And finally ... PHP.

Learn PHP quick and easy way by Larry Ullman is one of the best beginner PHP books ever written

You need to learn PHP, HTML & CSS

why you curious man..its not rocky science what programming should learn.The main thing is your interest.Interest is the main key for you.If you feel you good in PHP then starting PHP.

Php, HTML, CSS and some javascript

PHP is the only option you have when writing plugins for WP. Also check out the WP codex for some useful tips on how to use the hooks built in to WP.

Learn PHP, then wordpress customization will become easy

a membership to lynda.com may help you. great video tutorials on technical stuff.

I have written a plugin, I thought I was pretty good with PHP, but kinda struggled with wordpress plugins.

You should learn php language to make plugins in wordpress.

I don't know php, I am a java developer by profession but still I can make modifications to
existing scripts and plugins. It is not like where to learn PHP, it is how tp approach a
particular algorithm or a block. Language is all about syntax, but the annalysis matters.

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php for the backend programming then javascript for the frontend programming language

Seriously?

The answer can only be PHP + MySQL.

Add that with jQuery and you can create some awesome stuff.

I know HTML and often can make not complex modifications to wordpress. But definitely not ready for plugin development.

My understanding though is that the main thing is to have an idea what you would like to see your plugin does - and then simply outsource it. Of course if you have enough money to pay the programmer...

I too agree with DMS. But there is nothing wrong in just giving a lill try to the WP plugin development. The WP's codex site is more than enough to learn basic plugins..... You can find more on google.... Main Page « WordPress Codex

There are so meant php tutorials on the web, the best thing is to google php beginners tutorial and work your way from there.

I find it best to then set yourself a simple php driven task to help you learn. The fact tat you have a plugin in mind should help you focus on what you need to learn next.

Good luck :-)

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If you are going to purchase a book on PHP, I recommend one book.

murach's PHP and MYSQL - Training & Reference

I have a stack of php books and this one combines at least 5 of the ones I have in one reference. Meaning they have most of the content and code examples you need to get started in this one book.

It focuses only on PHP 5+ and MYSQLI connection method to MYSQL Databases. If u need other methods I just use google and usually end up at php.net and other results gogole comes back with for extended references.

But for first learning PHP I would go with this book from MURACH because they teach you the correct way to code from the get go. That way you never have to deal with spaghetti logic in your own programs. Meaning jumping around in basic loops and all code in one or two files.

Learn functions and classes, difference between FOR, FOREACH, WHILE and DO WHILE loops and how to assign to and remove variables and focus heavily studying how arrays works including multi-dimensional arrays.

Once you have that down then go learn how wordpress works, how it communicates and retrieves data from it's database and study the built-in functions wordpress has and how they work.

Then start writing plugins.

Starting from no knowledge about programming until you are proficient enough to start writing plugins to sell can take anywhere from one month to 3 months depending how quick you learn.

Easiest thing is to get good education on PHP and that book I suggest will take you most of the way there. Then it up to you to learn wordpress, it will be a bit different than what you learn in that book but you will have NO problems figuring it out.

If you do not want to spend money learning PHP, google is your best friend. Though there are a lot of people that don't know how to program very well teaching things that will confuse you if you don't already know the basics.