diff --git a/README.rst b/README.rst
index ca14835..16f6993 100644
--- a/README.rst
+++ b/README.rst
@@ -7,6 +7,7 @@ A library to convert between AQI value and pollutant concentration
 
 * United States Environmental Protection Agency (EPA)
 * China Ministry of Environmental Protection (MEP)
+* European Common Air Quality Index  (CAQI)
 
 .. image:: https://travis-ci.org/hrbonz/python-aqi.svg?branch=master
     :target: https://travis-ci.org/hrbonz/python-aqi
@@ -128,6 +129,7 @@ Resources
     * GB3095—2012 (2012/02/29) found at http://www.mep.gov.cn/gkml/hbb/bwj/201203/t20120302_224147.htm
     * HJ633-2012 (2012/02/29) found at http://www.zzemc.cn/em_aw/Content/HJ633-2012.pdf
 
+* CAQI: CAQI Air quality index https://www.airqualitynow.eu/download/CITEAIR-Comparing_Urban_Air_Quality_across_Borders.pdf
 
 License
 =======
diff --git a/aqi/__init__.py b/aqi/__init__.py
index 3d2dde7..d592af2 100644
--- a/aqi/__init__.py
+++ b/aqi/__init__.py
@@ -5,7 +5,8 @@
 from aqi.constants import (POLLUTANT_PM25, POLLUTANT_PM10,
                           POLLUTANT_O3_8H, POLLUTANT_O3_1H,
                           POLLUTANT_CO_8H, POLLUTANT_SO2_1H,
-                          POLLUTANT_NO2_1H, ALGO_EPA, ALGO_MEP)
+                          POLLUTANT_NO2_1H, ALGO_EPA, ALGO_MEP,
+                          ALGO_CAQI)
 
 from aqi.algos import get_algo, list_algos
 
diff --git a/aqi/algos/caqi.py b/aqi/algos/caqi.py
new file mode 100644
index 0000000..266afa3
--- /dev/null
+++ b/aqi/algos/caqi.py
@@ -0,0 +1,82 @@
+# -*- coding: utf-8 -*-
+
+from decimal import *
+
+from aqi.constants import (POLLUTANT_PM25, POLLUTANT_PM10,
+                           POLLUTANT_O3_1H, POLLUTANT_CO_8H, POLLUTANT_SO2_1H,
+                           POLLUTANT_NO2_1H)
+from aqi.algos.base import PiecewiseAQI
+
+
+class AQI(PiecewiseAQI):
+    """Implementation of the CAQI algorithm.
+    """
+
+    piecewise = {
+        'aqi': [
+            (Decimal(0), Decimal(24.99)),
+            (Decimal(25), Decimal(49.99)),
+            (Decimal(50), Decimal(74.99)),
+            (Decimal(75), Decimal(99.99)),
+            (Decimal(100), Decimal(1000))],
+        'bp': {
+            POLLUTANT_NO2_1H: [
+                (Decimal('0'), Decimal('49.99')),
+                (Decimal('50'), Decimal('99.99')),
+                (Decimal('100'), Decimal('199.99')),
+                (Decimal('200'), Decimal('399.99')),
+                (Decimal('400'), Decimal('inf')),
+            ],
+            POLLUTANT_O3_1H: [
+                (Decimal('0.0'), Decimal('60.000')),
+                (Decimal('60.001'), Decimal('120.000')),
+                (Decimal('120.001'), Decimal('180.000')),
+                (Decimal('180.001'), Decimal('240.000')),
+                (Decimal('240.001'), Decimal('inf')),
+            ],
+            POLLUTANT_PM10: [
+                (Decimal('0'), Decimal('25')),
+                (Decimal('25.01'), Decimal('50')),
+                (Decimal('50.01'), Decimal('90')),
+                (Decimal('90.01'), Decimal('180')),
+                (Decimal('180.01'), Decimal('inf')),
+            ],
+            POLLUTANT_PM25: [
+                (Decimal('0.0'), Decimal('15.0')),
+                (Decimal('15.01'), Decimal('30.0')),
+                (Decimal('30.01'), Decimal('55.0')),
+                (Decimal('55.01'), Decimal('110.0')),
+                (Decimal('110.01'), Decimal('inf')),
+            ],
+            POLLUTANT_CO_8H: [
+                (Decimal('0.0'), Decimal('5000.0')),
+                (Decimal('5000.01'), Decimal('7500.0')),
+                (Decimal('7500.01'), Decimal('10000.0')),
+                (Decimal('10000.01'), Decimal('20000.0')),
+                (Decimal('20000.01'), Decimal('inf')),
+            ],
+            POLLUTANT_SO2_1H: [
+                (Decimal('0'), Decimal('50')),
+                (Decimal('50.01'), Decimal('100')),
+                (Decimal('100.01'), Decimal('350')),
+                (Decimal('350.01'), Decimal('500')),
+                (Decimal('500.01'), Decimal('inf')),
+            ],
+        },
+        'prec': {
+            POLLUTANT_O3_1H: Decimal('.001'),
+            POLLUTANT_PM10: Decimal('.1'),
+            POLLUTANT_PM25: Decimal('.1'),
+            POLLUTANT_CO_8H: Decimal('.1'),
+            POLLUTANT_SO2_1H: Decimal('1.'),
+            POLLUTANT_NO2_1H: Decimal('1.'),
+        },
+        'units': {
+            POLLUTANT_O3_1H: 'µg/m³',
+            POLLUTANT_PM10: 'µg/m³',
+            POLLUTANT_PM25: 'µg/m³',
+            POLLUTANT_CO_8H: 'µg/m³',
+            POLLUTANT_SO2_1H: 'µg/m³',
+            POLLUTANT_NO2_1H: 'µg/m³',
+        },
+    }
diff --git a/aqi/constants.py b/aqi/constants.py
index 5ec0e99..b80ac05 100644
--- a/aqi/constants.py
+++ b/aqi/constants.py
@@ -16,3 +16,4 @@
 # constants for algorithms, canonical module name
 ALGO_EPA = 'aqi.algos.epa'
 ALGO_MEP = 'aqi.algos.mep'
+ALGO_CAQI = 'aqi.algos.caqi'