diff --git a/modules/otago-specific.xml b/modules/otago-specific.xml
index f13d23f..6e46323 100644
--- a/modules/otago-specific.xml
+++ b/modules/otago-specific.xml
@@ -27,4 +27,44 @@
 	</template>
 
 
+	<!--
+		Expand an Otago period code (e.g., "S1") into it's full equivalent (e.g., "Semester One").
+		
+		$period-code: The period code to be expanded.
+		
+		Returns: The expanded period string.
+	-->
+	<function name="infosci:expand-period-code" as="xs:string">
+		<common>
+			<xsl:param name="period-code" />
+			
+			<xsl:variable name="period-string">
+				<xsl:choose>
+					<xsl:when test="$period-code = 'SS'">
+						<xsl:text>Summer School</xsl:text>
+					</xsl:when>
+					<xsl:when test="$period-code = 'S1'">
+						<xsl:text>Semester One</xsl:text>
+					</xsl:when>
+					<xsl:when test="$period-code = 'S2'">
+						<xsl:text>Semester Two</xsl:text>
+					</xsl:when>
+					<xsl:when test="$period-code = 'FY'">
+						<xsl:text>Full Year</xsl:text>
+					</xsl:when>
+					<xsl:otherwise>
+						<xsl:message terminate="yes">
+							<xsl:text>Unrecognised period code "</xsl:text>
+							<xsl:value-of select="$period-code" />
+							<xsl:text>".</xsl:text>
+						</xsl:message>
+					</xsl:otherwise>
+				</xsl:choose>
+			</xsl:variable>
+			
+			<xsl:sequence select="$period-string" />
+		</common>
+	</function>
+	
+		
 </stylesheet>