diff --git a/doc/overview.md b/doc/overview.md
index d96ec9e..4403eaf 100644
--- a/doc/overview.md
+++ b/doc/overview.md
@@ -1,5 +1,89 @@
-How Everything Works
-====================
+Overview of MOTH
+================
+
+Monarch Of The Hill (MOTH) is a framework for running puzzle-based events for teams.
+Each team is assigned a token which they use to identify themselves.
+
+Teams are presented with a number of *categories*,
+each containing a sequence of *puzzles* of increasing point value.
+
+When the event starts, only the lowest-point puzzle in each category is available.
+As soon as any team enters the correct solution to the puzzle,
+the next puzzle is opened up for all teams.
+
+A scoreboard tracks team rankings,
+indicating score within each category,
+and overall ranking.
+
+
+How Scores are Calculated
+-------------------------
+
+The per-category score for team `t` is computed as:
+
+* Let `m` be the sum of all points in currently-visible puzzles in this category
+* Let `s` be the sum of all points team `t` has won in this category
+* Team `t`'s score is `s`/`m`
+
+Therefore, the maximum number of points a team can have in a category is 1.0.
+Put another way, a team's per-category score is the percentage of points they've made so far in that category.
+
+The total score for team `t` is the sum of all per-category points.
+
+Therefore, the maximum number of points a team can have in a 7-category event is 7.0.
+
+This point system has proven both easy to explain (if not immediately obvious),
+and acceptable by participants.
+Because we don't award extra points for quick responses,
+teams always feel like they have the possibility to catch up if they are skilled enough.
+
+
+Requirements
+-------------
+
+MOTH was written to run on a wide range of Linux systems.
+We are very careful not to require exotic extensions:
+you can run MOTH equally well on OpenWRT and Ubuntu Server.
+It might even run on BSD: if you've tried this, please email us!
+
+Its architecture also limits permissions,
+to make it easier to lock things down very tight.
+Since it writes to the filesystem slowly and atomically,
+it can be run from a USB flash drive formatted with VFAT.
+
+
+On the server, it requires:
+
+* Bourne shell (POSIX 1003.2: BASH is okay but not required)
+* Awk (POSIX 1003.2: gawk is okay but not required)
+* Lua 5.1
+
+
+On the client, it requires:
+
+* A modern web browser with JavaScript
+* Categories might add other requirements (like domain-specific tools to solve the puzzles)
+
+
+Filesystem Layout
+=================
+
+The system is set up to make it simple to run one or more contests on a single machine.
+
+I like to use `/srv/moth` as the base directory for all instances.
+So if I were running an instance called "hack",
+the instance directory would be `/srv/moth/hack`.
+
+There are five entries in each instance directory, described in detail below:
+
+    /srv/moth/hack                 # (r-x) Instance directory
+    /srv/moth/hack/assigned.txt    # (r--) List of assigned team tokens
+    /srv/moth/hack/bin/            # (r-x) Per-instance binaries
+    /srv/moth/hack/categories/     # (r-x) Installed categories
+    /srv/moth/hack/state/          # (rwx) Contest state
+    /srv/moth/hack/www/            # (r-x) Web server documentroot
+
+
 
 `assigned.txt`
 ----------------
@@ -12,7 +96,7 @@ and tell kids to use any number they want: it makes it quicker to start.
 For more advanced events,
 this doesn't work as well because people start guessing other teams' numbers to confuse each other.
 So I use hex representations of random 32-bit ints.
-But you could use anything you want in here (with some restrictions, detailed in the registration CGI).
+But you could use anything you want in here (for specifics on allowed characters, read the registration CGI).
 
 The registration CGI checks this list to see if a token has already assigned to a team name.
 Teams enter points by token,
@@ -21,10 +105,11 @@ Since we don't read their team name anywhere else than the registration and scor
 it allows some assumptions about what kind of strings tokens can be,
 resulting in simpler code.
 
-`packages/`
+
+`categories/`
 --------------
 
-`packages/` contains read-only package archives.
+`categories/` contains read-only category packages.
 Within each subdirectory there is:
 
 * `map.txt` mapping point values to directory names
@@ -33,6 +118,7 @@ Within each subdirectory there is:
 * `summary.txt` a compliation of `00summary.txt` files for puzzles, to give you a quick reference point when someone says "I need help on js 40".
 * `puzzles` is all the HTML that needs to be served up for the category
 
+
 `bin/`
 ------