Tack, what is it and what do I do with it?
What is all this "tack" stuff anyway?  Websters Dictionary simply defines tack as "stable gear".  I think we can define it a little more closely.  Tack is the equipment your horse wears to make it easier to handle and ride or drive him.  What do I do with it?  Well, today we will identify it.  Fitting and caring for tack will be it's own article.
Identify it
Tack falls into 6 main groupings.  We have halters, bridles, saddles, martingales, accessories and harness.
Halters
We can divide halters into two groups, stable halters and show halters.  Stable halters are made of leather, nylon, or rope.  They fit fairly loosly, and make it easier to catch, lead and tie the horse.  Some are made to break it the horse gets caught.  These are called breakaway halters. 
Show halters are used to control the horse in the show ring, and make his head look it's best. 
Western style show halters are made like stable halters.  They are leather, and often trimmed with silver or even gold.  the main difference is the fit.  A western show halter is closely fitted and designed to make the head look refined. 
English show halters look more like a bridle.  They are very fine leather, with a caveson and browband.  The browband and caveson are often made of colored patent leather.   Again, they are closely fitted, with the goal being to make the horse's head appear as refined as possible.
Arabian exhibitors have take the concept of refined an extra step, and invented the Arab "Thread".  This is a halter made of cable, which is extremely fine.  The idea is to have the halter look like it is barely there, while retaining the strength neccessary for control.
Of course, with every halter, we need a lead shank.  For everyday use, most people prefer round cotton or polyester ropes with a simple snap.  Some prefer a chain at the end for extra control.  Also available are nylon shanks, with or without chains, made to match the nylon halters.
Western style show leads are usually one inch leather, colored to match the halter, with a silver colored chain to match the trim on the halter.
English style show leads are usually a finer leather, often with a fine silver chain.  Occasionally, a rein will be buckles to the halter instead of a lead shank.
Arabian exhibitors also use the fine leather lead shanks with a very fine chain.
Bridles
Western bridles can have either a browband or an earpiece (split ear).  Many people today like the look of two earpieces.  Which you choose depends on the shape of your horse's head, and your own preferences.  The bridle may also have a throatlatch, or not.  The throatlatch halps prevent the bridle from sliding forward over the horse's ears. Western show bridles may NOT have a cavesson.  When showing, the bridle is usually decorated with silver or special horsehair ornaments.  The rider may use either split reins, or romal reins.
Hunt style bridles are usually made of fairly plain leather, although there may be some decorative stitching.  They have a browband, cavesson, and a throatlatch.  The reins are flat, and buckle at the ends.  They may be laced or braided to improve grip.  If using a pelham or double bridle, the reins are usually smooth.
Saddle Seat bridles are very fine, with patent leather on thebrowbands, and sometimes on the cavessons too.  They all have browbands, cavessons, and throatlatches.  A lip strap is also correct, but not required.  The reins are joined (buckled for snaffle reins, stitched for curb reins).
Dressage bridles are similar to Hunt style bridles.  They may, however, be padded or lined with a contrasting color of leather.  They also have a browband, cavesson, and throatlatch.  In addition, they may have an additional strap, run through a loop on the cavesson and around the horse's muzzle below the bit.  This is called a flash noseband and is legal for dressage.
Occasionally one will see a figure 8 noseband.  These are fairly common on Jumpers.  They go around the horses muzzle in an 8, with the intersection on the bridge of the nose.  A figure 8 is more effective in keeping the horse's mouth closed than an ordinary cavesson.
Bridles used on the trail may be any of these, or some combination that best suits the horse and rider.  There is one bridle made especially for trail riders.  It is called a halter/bridle, or simply a trail bridle or sometimes and Australian bridle..  It consists of a snugly fitted halter, and two cheekpieces which snap to the upper rings of the halter.  The bit is attached to the cheeks in the normal manner.  The advantage to this bridle is that if a trail rider wishes to stop and tie his horse, he simply unsnaps the cheeks, and ties the horse witht the halter.  The horse can easily be fed and watered with this arrangement as well.
Saddles
Saddles come in English and Western, right?  Well, sort of. . . .
Western saddles all have a heavier construction than English saddles.  They have fenders covering the stirrup leathers, a built up pommel and usually a horn.  They also tend ot have stamped or tooled leather and often silver decoration.  Beyond that, the saddle is as different as the job it is designed for.  Roping saddles have very solid forks and horns, but a low cantle to help the roper get off quickly when tying a calf.  Cutting saddles have deep seats and high cantles to hold the rider in place as the horse makes quick movements working the cow.  "Pleasure" or "Equitation" saddles should have deep seats, right in the center of the saddle to put the rider  straight over the horse's center of motion.  They should also have the stirrups hung directly under the rider, to aid the rider in maintaining good posture.  Game saddles are built forward, like a racing saddle.  They enable the rider to get his weight off the horse's back and let him run effectively.

English saddles have as much or more variety.  They are all built without a horn.  They use stirrup leathers and irons instead of fenders, and they tend to be smooth leather, without decoration.  Saddle Seat saddles are very flat, with cutback withers and have wider flaps.  The seat is placed so the rider sits farther back on the horse, allowing it to elevate it's forehand more easily.  Jumping saddles are the other extreme.  They are built very foreward, encouraging the rider off the horse's back, with his weight in the stirrups.  Older jumping saddles have large stuffed knee rolls, helping the rider stay in place.  Modern saddles use smaller knee rolls.  The knee rolls are often suede for extra grip.  Close contact saddles are popular right now for Hunter riders.  These saddles are also forward, although not as much as the Jumping saddle, but they have little or no knee roll.  The idea being to bring the rider's leg into close contact with the horse.  There are many  variations of Hunt Seat saddles, such as the hacking saddle, all purpose saddle, etc.  They are all more or less forward, and have more or less knee roll.  Dressage saddles are built more along the lines of the good equitation saddles.  They have a deep seat, with a long straight flap.  There may be a small knee roll and sometimes also a small thigh block to aid the rider in maintaining the most effective position on the horse.

Finally ,we have Australian Saddles.  These saddles seem to us to be a cross between the English and the Western saddle, but in fact, they were created out of the older style english saddles for the uses to which we put western saddles.  They have deep seats for stability but more bulk and longer bars, spreading out the rider's weight on the horse's back.  Some have a horn, and some do not.
Martingales
Martingales have one basic purpose, to keep the horse's head in a position where the rider can easily affect it  for control.  Many have secondary purposes as well, but this is the main one.
Standing Martingale.  Western riders call this one a Tie Down.  It's primary purpose is to keep the horse's head out of the rider's face.  This is done by attaching a strap to the cavesson, or to a seperate headstall for a western rider.  The strap goes between the front legs and attaches to the girth or cinch.  It may also be a shorter strap which attaches to a breastplate.  Most commonly seen on hunters over fences, game horses, and rope horses.  Hunters may depend on it for balance when landing over a fence.  Rope and game horses often use it to run against  when running hard.  Tie downs are made with a variety of headstalls affecting the horse's nose or his poll.
Running Martingale.  Or, in Western speak, a training fork.  A bit more versatile, the running martingale has two rings, through which the reins run, connected to two leather straps which join at about the height of the horse's chest and either fasten to the breast collar or continue on to the girth or cinch.  This should only be used with a snaffle bridle for safety, as it creates leverage, and can become very severe used with a curb.  The principle is that if the horse is carrying his head correctly, the martingale puts no pressure on the reins.  If he raises his head too high, the martingale allows the rider's rein use to have a downward pull to it, thereby reminding the horse which direction to go with his head.  Legal on Jumpers, Game horses, and some driving horses, this is mainly a training tool.
German or Olympic martingale.  This martingale requires special reins with rings on them at close intervals.  The martingale comes up from the breastcollar or girth, throught the rings of the snaffle (again, too much leverage with a curb) and snaps to a ring on each rein.  This is a powerful training tool as if the horses is behaving, the snaffle reins act in their normal fashion, however, if the horse begins to bore his nose out or throw his head up, the martingale acts as a draw rein.  This gives the rider a gread deal of leverage, but only to the point where the martingale is set.  Properly adjusted, and used under experienced supervision, this martingale is safe for less experienced riders who should not use draw reins at all.  Strictly a training too (although I think I have seen them on Jumpers).
Irish martingale.  This one is pretty obscure.  It is a little strap, about 4" long with a ring at each end.   A rein goes through each ring under the horse's neck.  It's sole use is to keep one rein on each side of the neck and is used by steeplechase riders and some eventers.
Accessories
The main accessories are saddle pads and breastcollars. Cruppers may also be included.
Saddle pads come in many shapes to suit the various shapes of saddles.  The main purpose of the pad is to protect the horse from the saddle and the saddle from the horse.  Saddle seat horses are traditionaly ridden without pads, although there is no rule prohibition them.  Hunt seat horses were shown without pads in the past, but now most use the white fleese pads for showing.  In Dressage, a squared off quilted cotton pad is traditional, most commonly white.  Western uses a variety of blankets and stuffed pads.  In addition, there are many felt or horse hair pads, in addition to "orthapedic" or "gel" or foam pads that are designed to be put under the pretty pad and do the real work.  If your saddle fits your horse perfectly, the only reason to have a pad is to wick away sweat from the horse's back and  keep the underside of the saddle clean.  If your saddle doesn't fit perfectly. . . . .ah but that is a topic for another article. . .
Breastcollars come in several different designs, but all have the purpose fo keeping the saddle from slipping backwards.  They attach to d rings on the front of the saddle and to the girth or cinch (usually).  They may or may not have a strap which goes over the withers to keep them from sagging.  Many western riders use them in the show ring to provide the "look" or provide an extra place to hang silver.
A Crupper is a strap from the back of the saddle to a padded tail piece which fits under the horse's dock.  It's purppose is to keep the saddle from sliding forward.  This can be useful on a mutton withered horse, or on any horse if treking in the mountains.
Harness
Harness is used to pull things, a cart, a buggy, a sleigh or a plow.  There are three basic types, with many variations.
Fine harness.  This harness is used in Pleasure Driving, Fine Harness, and Park classes at horse shows.  It has an overcheck (usually, sometimes a side check), a light breastcollar, an running martingale, and uses wrap straps or thimbles to stop the light weight cart or buggy.  This harness is made with a lot of patent leather often in red or other colors.and is very fine, so as to show off the elegant horse.
Carriage harness.  You will see this one in Carriage Driving classes and only ocasionaly in Pleasure Driving.  There is usually no check, but sometimes a side check is seen.  It may have a breastcollar or a "full" or neck collar.  The harness will have breeching to stop the wooden wheeled cart or buggy.  There will be no martingale.  This harness is heavier than the fine harness but not extremely heavy.  Those made for the show ring will also have a lot of patent leather, but not usually in colors.
Draft harness.  There are also variations to this one, but we will put them all together for our purposes here.  This is a very heavy harness, with a full collar.  It will have breeching and either a side check or no check.  The traces on these harness often end in heel chains for hooking to machinery or heavy wagons.  The fancy collars which are seen on the show versions are highly decorated and may weigh over 100 pounds!
Pictures and more information are coming folks, but I am out of time right now.  If you have a diagram with parts marked of any of these items that I can post here, please let me know!