diff --git a/inc/class.semester.inc b/inc/class.semester.inc
new file mode 100644
--- /dev/null
+++ b/inc/class.semester.inc
@@ -0,0 +1,176 @@
+<?php
+/*
+ * Copyright 2010 Nathan Phillip Brink <ohnobinki@ohnopublishing.net>
+ *
+ * This file is a part of slate_permutate.
+ *
+ * slate_permutate is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * slate_permutate is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with slate_permutate.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+$root_dir = dirname(__FILE__) . DIRECTORY_SEPARATOR . '..' . DIRECTORY_SEPARATOR;
+require_once($root_dir . 'class.class.php');
+require_once($root_dir . 'class.section.php');
+
+/**
+ * \brief
+ *   Identifies a school semester and acts as a container for courses
+ *   offered in a semester.
+ */
+class Semester
+{
+  /**
+   * \brief
+   *   The Fall season.
+   */
+  const SEASON_FALL = 'fall';
+
+  /**
+   * \brief
+   *   The Spring season.
+   */
+  const SEASON_SPRING = 'spring';
+
+  /**
+   * \brief
+   *   Instantiate an empty Semester.
+   *
+   * \param $year
+   *   The year of this semester. Must be four digits.
+   * \param $season
+   *   The season of this semester. Currently, only
+   *   Semester::SEASON_SPRING and Semester::SEASON_FALL are valid.
+   */
+  function __construct($year, $season)
+  {
+    if (!in_array($season, array(self::SEASON_SPRING, self::SEASON_FALL)))
+      throw new ErrorException('Attempt to construct a Semester with a $season which is neither Semester::SEASON_SPRING nor Semester::SEASON_FALL. `' . $season . '\' was given.');
+    $this->season = $season;
+
+    if (strlen($year) != 4)
+      throw new ErrorException('Attempt to construct a Semester with an invalid year. The given year is `' . $year . '\'');
+    $this->year = $year;
+
+    $this->departments = array();
+  }
+
+  /**
+   * \brief
+   *   Add a class to this Semester.
+   *
+   * \param $class
+   *   The class/course to add.
+   */
+  public function class_add(Classes $class)
+  {
+    $class_parts = Classes::parse($class->getName());
+    if (!isset($class_parts['course']))
+      throw ErrorException('I was given a class with an invalid name: `' . $class->getName() . '\'');
+
+    if (!isset($this->departments[$class_parts['department']]))
+      $this->departments[$class_parts['department']] = array();
+    $department =& $this->departments[$class_parts['department']];
+
+    $department[$class_parts['course']] = $class;
+  }
+
+  /**
+   * \brief
+   *   Retrieve a class.
+   *
+   * \param $dept
+   *   The class's department. 'CS' for 'CS-262'.
+   * \param $class
+   *   The course/class number. '262' for 'cs-262'.
+   * \return
+   *   A Classes or NULL if not found.
+   */
+  public function class_get($dept, $class)
+  {
+    if (!isset($this->departments[$dept][$class]))
+      return NULL;
+
+    return $this->departments[$dept][$class];
+  }
+
+  /**
+   * \brief
+   *   Gets a list of departments available in this semester.
+   */
+  public function departments_get()
+  {
+    return array_keys($this->departments);
+  }
+
+  /**
+   * \brief
+   *   Gets a list of class/course numbers available for a particular
+   *   department.
+   */
+  public function department_classes_get($dept)
+  {
+    if (!isset($this->departments[$dept]))
+      throw new ErrorException('I was asked for a department I don\'t own: ' . $dept);
+
+    return array_keys($this->departments[$dept]);
+  }
+
+  /**
+   * \brief
+   *   Utility function to add a section to the semester,
+   *   automatically creating classes as necessary.
+   *
+   * \param $dept
+   *   The department this section belongs to.
+   * \param $class
+   *   The class this section belongs to.
+   * \param $section
+   *   The section itself.
+   */
+  public function section_add($dept, $class, Section $section)
+  {
+    $dept = strtoupper($dept);
+    $class = strtoupper($class);
+
+    if (!isset($this->departments[$dept])
+	|| !isset($this->departments[$dept][$class]))
+      {
+	$classobj = new Classes($dept . '-' . $class);
+	$this->class_add($classobj);
+      }
+    else
+      {
+	$classobj = $this->departments[$dept][$class];
+      }
+
+    $classobj->section_add($section);
+  }
+
+  /**
+   * \brief
+   *   Get a semester's year.
+   */
+  public function year_get()
+  {
+    return $this->year;
+  }
+
+  /**
+   * \brief
+   *   Get a semester's season.
+   */
+  public function season_get()
+  {
+    return $this->season;
+  }
+}