diff --git a/chrono/datetime.cpp b/chrono/datetime.cpp
index f396e1e..979260f 100644
--- a/chrono/datetime.cpp
+++ b/chrono/datetime.cpp
@@ -528,4 +528,78 @@ DateTimeExpression DateTimeExpression::fromString(const char *str)
     return res;
 }
 
+/*!
+ * \brief Returns the string representation of the current instance in the ISO format.
+ * \remarks Only present parts will be included.
+ */
+std::string DateTimeExpression::toIsoString(char dateDelimiter, char timeDelimiter, char timeZoneDelimiter) const
+{
+    auto s = std::stringstream(std::stringstream::in | std::stringstream::out);
+    s << setfill('0');
+    if (parts & DateTimeParts::Year) {
+        s << setw(4) << value.year();
+    }
+    if (parts & DateTimeParts::Month) {
+        if (s.tellp()) {
+            s << dateDelimiter;
+        }
+        s << setw(2) << value.month();
+    }
+    if (parts & DateTimeParts::Day) {
+        if (s.tellp()) {
+            s << dateDelimiter;
+        }
+        s << setw(2) << value.day();
+    }
+    if (parts & DateTimeParts::Hour) {
+        if (s.tellp()) {
+            s << 'T';
+        }
+        s << setw(2) << value.hour();
+    }
+    if (parts & DateTimeParts::Minute) {
+        if (s.tellp()) {
+            s << timeDelimiter;
+        }
+        s << setw(2) << value.minute();
+    }
+    if (parts & DateTimeParts::Second) {
+        if (s.tellp()) {
+            s << timeDelimiter;
+        }
+        s << setw(2) << value.second();
+    }
+    if (parts & DateTimeParts::SubSecond) {
+        const auto milli = value.millisecond();
+        const auto micro = value.microsecond();
+        const auto nano = value.nanosecond();
+        s << '.' << setw(3) << milli;
+        if (micro || nano) {
+            s << setw(3) << micro;
+            if (nano) {
+                s << nano / TimeSpan::nanosecondsPerTick;
+            }
+        }
+    }
+    if (parts & DateTimeParts::TimeZoneDelta) {
+        auto d = delta;
+        if (d.isNegative()) {
+            s << '-';
+            d = TimeSpan(-d.totalTicks());
+        } else {
+            s << '+';
+        }
+        if (parts & DateTimeParts::DeltaHour) {
+            s << setw(2) << d.hours();
+        }
+        if (parts & DateTimeParts::DeltaMinute) {
+            if (parts & DateTimeParts::DeltaHour) {
+                s << timeZoneDelimiter;
+            }
+            s << setw(2) << d.minutes();
+        }
+    }
+    return s.str();
+}
+
 } // namespace CppUtilities
diff --git a/chrono/datetime.h b/chrono/datetime.h
index 863ebd8..33beefb 100644
--- a/chrono/datetime.h
+++ b/chrono/datetime.h
@@ -166,6 +166,8 @@ struct CPP_UTILITIES_EXPORT DateTimeExpression {
     DateTimeParts parts = DateTimeParts::None; /**< The parts present in the expression as flag enum. */
 
     constexpr DateTime gmt() const;
+    constexpr bool operator==(const DateTimeExpression &other) const;
+    std::string toIsoString(char dateDelimiter = '-', char timeDelimiter = ':', char timeZoneDelimiter = ':') const;
     static DateTimeExpression fromIsoString(const char *str);
     static DateTimeExpression fromString(const char *str);
 };
@@ -178,6 +180,14 @@ constexpr DateTime DateTimeExpression::gmt() const
     return value - delta;
 }
 
+/*!
+ * \brief Returns whether the expressions are equivalent.
+ */
+constexpr bool DateTimeExpression::operator==(const DateTimeExpression &other) const
+{
+    return value == other.value && delta == other.delta && parts == other.parts;
+}
+
 /*!
  * \brief Constructs a DateTime.
  */
diff --git a/tests/chronotests.cpp b/tests/chronotests.cpp
index 9294ce4..38c6e12 100644
--- a/tests/chronotests.cpp
+++ b/tests/chronotests.cpp
@@ -230,44 +230,53 @@ void ChronoTests::testDateTime()
  */
 void ChronoTests::testDateTimeExpression()
 {
-    // check adding ISO timestamp parts one-by-one
+    // check adding ISO timestamp parts one-by-one and serialization back to string
     auto expr = DateTimeExpression::fromIsoString("1");
     auto parts = DateTimeParts::Year;
     CPPUNIT_ASSERT_EQUAL(DateTime(), expr.value);
     CPPUNIT_ASSERT_EQUAL(TimeSpan(), expr.delta);
     CPPUNIT_ASSERT_EQUAL(parts, expr.parts);
+    CPPUNIT_ASSERT_EQUAL("0001"s, expr.toIsoString());
     expr = DateTimeExpression::fromIsoString("1-1");
     CPPUNIT_ASSERT_EQUAL(DateTime(), expr.value);
     CPPUNIT_ASSERT_EQUAL(TimeSpan(), expr.delta);
     CPPUNIT_ASSERT_EQUAL(parts |= DateTimeParts::Month, expr.parts);
+    CPPUNIT_ASSERT_EQUAL("0001-01"s, expr.toIsoString());
     expr = DateTimeExpression::fromIsoString("1-1-1");
     CPPUNIT_ASSERT_EQUAL(DateTime(), expr.value);
     CPPUNIT_ASSERT_EQUAL(TimeSpan(), expr.delta);
     CPPUNIT_ASSERT_EQUAL(parts |= DateTimeParts::Day, expr.parts);
+    CPPUNIT_ASSERT_EQUAL("0001-01-01"s, expr.toIsoString());
     expr = DateTimeExpression::fromIsoString("1-1-1T0");
     CPPUNIT_ASSERT_EQUAL(DateTime(), expr.value);
     CPPUNIT_ASSERT_EQUAL(TimeSpan(), expr.delta);
     CPPUNIT_ASSERT_EQUAL(parts |= DateTimeParts::Hour, expr.parts);
+    CPPUNIT_ASSERT_EQUAL("0001-01-01T00"s, expr.toIsoString());
     expr = DateTimeExpression::fromIsoString("1-1-1T0:0");
     CPPUNIT_ASSERT_EQUAL(DateTime(), expr.value);
     CPPUNIT_ASSERT_EQUAL(TimeSpan(), expr.delta);
     CPPUNIT_ASSERT_EQUAL(parts |= DateTimeParts::Minute, expr.parts);
+    CPPUNIT_ASSERT_EQUAL("0001-01-01T00:00"s, expr.toIsoString());
     expr = DateTimeExpression::fromIsoString("1-1-1T0:0:0");
     CPPUNIT_ASSERT_EQUAL(DateTime(), expr.value);
     CPPUNIT_ASSERT_EQUAL(TimeSpan(), expr.delta);
     CPPUNIT_ASSERT_EQUAL(parts |= DateTimeParts::Second, expr.parts);
+    CPPUNIT_ASSERT_EQUAL("0001-01-01T00:00:00"s, expr.toIsoString());
     expr = DateTimeExpression::fromIsoString("1-1-1T0:0:0.0");
     CPPUNIT_ASSERT_EQUAL(DateTime(), expr.value);
     CPPUNIT_ASSERT_EQUAL(TimeSpan(), expr.delta);
     CPPUNIT_ASSERT_EQUAL(parts |= DateTimeParts::SubSecond, expr.parts);
+    CPPUNIT_ASSERT_EQUAL("0001-01-01T00:00:00.000"s, expr.toIsoString());
     expr = DateTimeExpression::fromIsoString("1-1-1T0:0:0.0+0");
     CPPUNIT_ASSERT_EQUAL(DateTime(), expr.value);
     CPPUNIT_ASSERT_EQUAL(TimeSpan(), expr.delta);
     CPPUNIT_ASSERT_EQUAL(parts |= DateTimeParts::DeltaHour, expr.parts);
+    CPPUNIT_ASSERT_EQUAL("0001-01-01T00:00:00.000+00"s, expr.toIsoString());
     expr = DateTimeExpression::fromIsoString("1-1-1T0:0:0.0-0:0");
     CPPUNIT_ASSERT_EQUAL(DateTime(), expr.value);
     CPPUNIT_ASSERT_EQUAL(TimeSpan(), expr.delta);
     CPPUNIT_ASSERT_EQUAL(parts |= DateTimeParts::DeltaMinute, expr.parts);
+    CPPUNIT_ASSERT_EQUAL("0001-01-01T00:00:00.000+00:00"s, expr.toIsoString());
 
     // check that omitting parts in the middle is not possible anyways
     CPPUNIT_ASSERT_THROW(DateTimeExpression::fromIsoString("1-1T0"), ConversionException);