Hello
I am working on a circuit with an 18v battery that I am stepping down to 12v to go into a small controller. The 12v regulator has an input, output, and ground. So I am planning on passing the regulator's ground into the negative terminal of the battery, pretty straight forward. But then I'm passing the Vout into the controller and the controller also has a ground so can I pass the controller's ground into the batteries negative terminal as well? Wish I had a better way to illustrate this.
All grounds need to be tied together..
It's all about the potential difference between 2 voltage sources.
You seem to have the situation under control
Wish I had a better way to illustrate this.
Do what I do a lot - draw it up in Powerpoint/Open Office equivalent, save it as a .jpg, and attach that here.
Or get a real schematic capture tool. www.expresspcb.com is wonderfu for making drawings/schematics to post here, easy to use & free.
CrossRoads:
www.expresspcb.com is wonderfu for making drawings/schematics to post here, easy to use & free.
I'll second that- takes about 5min to master and very easy to create your own components.
Truly "wonderfu" [sic] 
It is a convention derived from the use of valve radios and automotive electrics (I had a car radio at one time, which was a hybrid which had valves operating at 12V B+ as well as a transistor audio amplifier) that the negative is ground and the vast majority of systems follow this, the prime exception being wired telephone systems (50V positive ground).
Paul__B:
It is a convention derived from the use of valve radios and automotive electrics (I had a car radio at one time, which was a hybrid which had valves operating at 12V B+ as well as a transistor audio amplifier) that the negative is ground and the vast majority of systems follow this, the prime exception being wired telephone systems (50V positive ground).
And old cars with dynamos which also have a positive ground.
ChilliTronix:
And old cars with dynamos which also have a positive ground.
Yes, well, there are a lot of them!
Thanks for all the help everyone! 
Ill surely be looking into a better way to post schematics, but I'm glad it made sense to you anyways!
Paul__B:
It is a convention derived from the use of valve radios and automotive electrics (I had a car radio at one time, which was a hybrid which had valves operating at 12V B+ as well as a transistor audio amplifier) that the negative is ground and the vast majority of systems follow this, the prime exception being wired telephone systems (50V positive ground).
Negative isn't ground in a system with both positive and negative rails...
Ground is ground, its the reference point, you choose it according to your purposes.
It you want a 12V regulated supply from an 18V battery you can either use a +12V
regulator and negative ground, or a -12V regulator and +ve ground. Most single
rail applications are negative ground these days, partly a legacy of valve electronics
and partly a legacy of TTL, both of which have control input voltages closer to the
-ve rail than the +ve rail, making the negative supply a natural ground reference for
signal voltages. Modern CMOS chips are basically symmetric but have inherited the
convention for ground to be the negative rail.
I've an old (really old) book on transistor circuits and they use the positive ground
convention and PNP transistors predominantly, since they were more easily made
in the days of germanium.
MarkT:
I've an old (really old) book on transistor circuits and they use the positive ground convention and PNP transistors predominantly, since they were more easily made
in the days of germanium.
OC71!