diff --git a/opentelemetry-sdk/CHANGELOG.md b/opentelemetry-sdk/CHANGELOG.md
index 19dac050a4..6abe299a6f 100644
--- a/opentelemetry-sdk/CHANGELOG.md
+++ b/opentelemetry-sdk/CHANGELOG.md
@@ -26,6 +26,7 @@
   - `shutdown` methods in `LoggerProvider` and `LogProcessor` now takes a immutable reference
   - After `shutdown`, `LoggerProvider` will return noop `Logger`
   - After `shutdown`, `LogProcessor` will not process any new logs
+- [#1644](https://github.com/open-telemetry/opentelemetry-rust/pull/1644) Fix cumulative aggregation for observable counters.
 
 ## v0.22.1
 
diff --git a/opentelemetry-sdk/src/metrics/internal/sum.rs b/opentelemetry-sdk/src/metrics/internal/sum.rs
index 83a6b07858..6997907253 100644
--- a/opentelemetry-sdk/src/metrics/internal/sum.rs
+++ b/opentelemetry-sdk/src/metrics/internal/sum.rs
@@ -1,3 +1,4 @@
+use std::marker::PhantomData;
 use std::sync::atomic::{AtomicBool, Ordering};
 use std::{
     collections::{hash_map::Entry, HashMap},
@@ -14,30 +15,56 @@ use super::{
     AtomicTracker, Number,
 };
 
+/// Abstracts the update operation for a measurement.
+trait UpdateOperation<T> {
+    fn update(a: &mut T, b: T);
+}
+
+struct AddAssign;
+
+impl<T> UpdateOperation<T> for AddAssign
+where
+    T: std::ops::AddAssign<T>,
+{
+    fn update(a: &mut T, b: T) {
+        *a += b
+    }
+}
+
+struct Assign;
+
+impl<T> UpdateOperation<T> for Assign {
+    fn update(a: &mut T, b: T) {
+        *a = b
+    }
+}
+
 /// The storage for sums.
-struct ValueMap<T: Number<T>> {
+struct ValueMap<T: Number<T>, O> {
     values: Mutex<HashMap<AttributeSet, T>>,
     has_no_value_attribute_value: AtomicBool,
     no_attribute_value: T::AtomicTracker,
+    _operation: PhantomData<O>,
 }
 
-impl<T: Number<T>> Default for ValueMap<T> {
+impl<T: Number<T>, O: UpdateOperation<T>> Default for ValueMap<T, O> {
     fn default() -> Self {
         ValueMap::new()
     }
 }
 
-impl<T: Number<T>> ValueMap<T> {
+impl<T: Number<T>, O: UpdateOperation<T>> ValueMap<T, O> {
     fn new() -> Self {
         ValueMap {
             values: Mutex::new(HashMap::new()),
             has_no_value_attribute_value: AtomicBool::new(false),
             no_attribute_value: T::new_atomic_tracker(),
+            _operation: PhantomData,
         }
     }
 }
 
-impl<T: Number<T>> ValueMap<T> {
+impl<T: Number<T>, O: UpdateOperation<T>> ValueMap<T, O> {
     fn measure(&self, measurement: T, attrs: AttributeSet) {
         if attrs.is_empty() {
             self.no_attribute_value.add(measurement);
@@ -47,8 +74,8 @@ impl<T: Number<T>> ValueMap<T> {
             let size = values.len();
             match values.entry(attrs) {
                 Entry::Occupied(mut occupied_entry) => {
-                    let sum = occupied_entry.get_mut();
-                    *sum += measurement;
+                    let value = occupied_entry.get_mut();
+                    O::update(value, measurement);
                 }
                 Entry::Vacant(vacant_entry) => {
                     if is_under_cardinality_limit(size) {
@@ -56,7 +83,7 @@ impl<T: Number<T>> ValueMap<T> {
                     } else {
                         values
                             .entry(STREAM_OVERFLOW_ATTRIBUTE_SET.clone())
-                            .and_modify(|val| *val += measurement)
+                            .and_modify(|val| O::update(val, measurement))
                             .or_insert(measurement);
                         global::handle_error(MetricsError::Other("Warning: Maximum data points for metric stream exceeded. Entry added to overflow.".into()));
                     }
@@ -68,7 +95,7 @@ impl<T: Number<T>> ValueMap<T> {
 
 /// Summarizes a set of measurements made as their arithmetic sum.
 pub(crate) struct Sum<T: Number<T>> {
-    value_map: ValueMap<T>,
+    value_map: ValueMap<T, AddAssign>,
     monotonic: bool,
     start: Mutex<SystemTime>,
 }
@@ -232,7 +259,7 @@ impl<T: Number<T>> Sum<T> {
 
 /// Summarizes a set of pre-computed sums as their arithmetic sum.
 pub(crate) struct PrecomputedSum<T: Number<T>> {
-    value_map: ValueMap<T>,
+    value_map: ValueMap<T, Assign>,
     monotonic: bool,
     start: Mutex<SystemTime>,
     reported: Mutex<HashMap<AttributeSet, T>>,
@@ -367,11 +394,6 @@ impl<T: Number<T>> PrecomputedSum<T> {
                 .data_points
                 .reserve_exact(n - s_data.data_points.capacity());
         }
-        let mut new_reported = HashMap::with_capacity(n);
-        let mut reported = match self.reported.lock() {
-            Ok(r) => r,
-            Err(_) => return (0, None),
-        };
 
         if self
             .value_map
@@ -387,24 +409,16 @@ impl<T: Number<T>> PrecomputedSum<T> {
             });
         }
 
-        let default = T::default();
         for (attrs, value) in values.iter() {
-            let delta = *value - *reported.get(attrs).unwrap_or(&default);
-            if delta != default {
-                new_reported.insert(attrs.clone(), *value);
-            }
             s_data.data_points.push(DataPoint {
                 attributes: attrs.clone(),
                 start_time: Some(prev_start),
                 time: Some(t),
-                value: delta,
+                value: *value,
                 exemplars: vec![],
             });
         }
 
-        *reported = new_reported;
-        drop(reported); // drop before values guard is dropped
-
         (
             s_data.data_points.len(),
             new_agg.map(|a| Box::new(a) as Box<_>),
diff --git a/opentelemetry-sdk/src/metrics/mod.rs b/opentelemetry-sdk/src/metrics/mod.rs
index 80ff89469b..6ad1c15fc0 100644
--- a/opentelemetry-sdk/src/metrics/mod.rs
+++ b/opentelemetry-sdk/src/metrics/mod.rs
@@ -72,6 +72,7 @@ mod tests {
         KeyValue,
     };
     use std::borrow::Cow;
+    use std::sync::{Arc, Mutex};
 
     // "multi_thread" tokio flavor must be used else flush won't
     // be able to make progress!
@@ -980,4 +981,190 @@ mod tests {
                 .expect("Failed to cast aggregation to expected type")
         }
     }
+
+    /// Observable counter in delta aggregation.
+    ///
+    /// ObservableCounter provides the current (i.e cumulative) value of the counter at the time of observation,
+    /// and the SDK is expected to remember the previous value, so that it can do cumulative to
+    /// delta conversion.
+    #[tokio::test(flavor = "multi_thread")]
+    async fn observable_counter_delta() {
+        // cargo test observable_counter_delta --features=metrics,testing  -- --nocapture
+
+        // Arrange
+        let test_context = TestContext::new(Some(Temporality::Delta));
+        let meter_provider = test_context.meter_provider;
+        let exporter = test_context.exporter;
+        let meter = meter_provider.meter("test");
+        let observable_counter = meter.u64_observable_counter("my_observable_counter").init();
+
+        // Act
+        // The Observable counter reports 100, 200, 300 and so on.
+        let i = Arc::new(Mutex::new(0));
+        meter
+            .register_callback(&[observable_counter.as_any()], move |observer| {
+                let mut num = i.lock().unwrap();
+                *num += 1;
+
+                println!("Observable Counter is reporting: {}", *num * 100);
+
+                observer.observe_u64(
+                    &observable_counter,
+                    *num * 100,
+                    [
+                        KeyValue::new("statusCode", "200"),
+                        KeyValue::new("verb", "get"),
+                    ]
+                    .as_ref(),
+                );
+            })
+            .expect("Expected to register callback");
+
+        meter_provider.force_flush().unwrap();
+
+        // Assert
+        let resource_metrics = exporter
+            .get_finished_metrics()
+            .expect("metrics are expected to be exported.");
+        assert!(!resource_metrics.is_empty());
+        let metric = &resource_metrics[0].scope_metrics[0].metrics[0];
+        assert_eq!(metric.name, "my_observable_counter");
+
+        let sum = metric
+            .data
+            .as_any()
+            .downcast_ref::<data::Sum<u64>>()
+            .expect("Sum aggregation expected for ObservableCounter instruments by default");
+
+        assert_eq!(
+            sum.temporality,
+            data::Temporality::Delta,
+            "Should produce Delta as configured."
+        );
+
+        assert_eq!(sum.data_points.len(), 1);
+
+        // find and validate the single datapoint
+        let data_point = &sum.data_points[0];
+        assert_eq!(data_point.value, 100);
+
+        // Flush again, to trigger next collection.
+        exporter.reset();
+        meter_provider.force_flush().unwrap();
+
+        // Assert
+        let resource_metrics = exporter
+            .get_finished_metrics()
+            .expect("metrics are expected to be exported.");
+        assert!(!resource_metrics.is_empty());
+        let metric = &resource_metrics[0].scope_metrics[0].metrics[0];
+        assert_eq!(metric.name, "my_observable_counter");
+
+        let sum = metric
+            .data
+            .as_any()
+            .downcast_ref::<data::Sum<u64>>()
+            .expect("Sum aggregation expected for ObservableCounter instruments by default");
+
+        assert_eq!(sum.data_points.len(), 1);
+
+        // find and validate the single datapoint
+        let data_point = &sum.data_points[0];
+
+        // The second observation should be 100 as well, as temporality is delta
+        assert_eq!(data_point.value, 100);
+    }
+
+    /// Tests Observable counter in cumulative aggregation.
+    ///
+    /// ObservableCounter provides the current (i.e Cumulative) value of the counter at the time of observation,
+    /// and the SDK is expected to aggregate the value as-is.
+    #[tokio::test(flavor = "multi_thread", worker_threads = 1)]
+    async fn observable_counter_cumulative() {
+        // cargo test observable_counter_cumulative --features=metrics,testing -- --nocapture
+
+        // Arrange
+        let test_context = TestContext::new(Some(Temporality::Cumulative));
+        let meter_provider = test_context.meter_provider;
+        let exporter = test_context.exporter;
+        let meter = meter_provider.meter("test");
+        let observable_counter = meter.u64_observable_counter("my_observable_counter").init();
+
+        // Act
+        // The Observable counter reports 100, 200, 300 and so on.
+        let i = Arc::new(Mutex::new(0));
+        meter
+            .register_callback(&[observable_counter.as_any()], move |observer| {
+                let mut num = i.lock().unwrap();
+                *num += 1;
+
+                println!("Observable Counter is reporting: {}", *num * 100);
+
+                observer.observe_u64(
+                    &observable_counter,
+                    *num * 100,
+                    [
+                        KeyValue::new("statusCode", "200"),
+                        KeyValue::new("verb", "get"),
+                    ]
+                    .as_ref(),
+                );
+            })
+            .expect("Expected to register callback");
+
+        meter_provider.force_flush().unwrap();
+
+        // Assert
+        let resource_metrics = exporter
+            .get_finished_metrics()
+            .expect("metrics are expected to be exported.");
+        assert!(!resource_metrics.is_empty());
+        let metric = &resource_metrics[0].scope_metrics[0].metrics[0];
+        assert_eq!(metric.name, "my_observable_counter");
+
+        let sum = metric
+            .data
+            .as_any()
+            .downcast_ref::<data::Sum<u64>>()
+            .expect("Sum aggregation expected for ObservableCounter instruments by default");
+
+        assert_eq!(
+            sum.temporality,
+            data::Temporality::Cumulative,
+            "Should produce Cumulative by default."
+        );
+
+        assert_eq!(sum.data_points.len(), 1);
+
+        // find and validate the single datapoint
+        let data_point = &sum.data_points[0];
+        // 100 is the first observation.
+        assert_eq!(data_point.value, 100);
+
+        // Flush again, to trigger next collection.
+        exporter.reset();
+        meter_provider.force_flush().unwrap();
+
+        // Assert
+        let resource_metrics = exporter
+            .get_finished_metrics()
+            .expect("metrics are expected to be exported.");
+
+        assert!(!resource_metrics.is_empty());
+        let metric = &resource_metrics[0].scope_metrics[0].metrics[0];
+        assert_eq!(metric.name, "my_observable_counter");
+
+        let sum = metric
+            .data
+            .as_any()
+            .downcast_ref::<data::Sum<u64>>()
+            .expect("Sum aggregation expected for ObservableCounter instruments by default");
+
+        assert_eq!(sum.data_points.len(), 1);
+
+        // find and validate the single datapoint
+        let data_point = &sum.data_points[0];
+        // The second observation should be 200
+        assert_eq!(data_point.value, 200);
+    }
 }
diff --git a/opentelemetry/src/metrics/instruments/counter.rs b/opentelemetry/src/metrics/instruments/counter.rs
index c10ac70405..33439182b1 100644
--- a/opentelemetry/src/metrics/instruments/counter.rs
+++ b/opentelemetry/src/metrics/instruments/counter.rs
@@ -82,7 +82,7 @@ impl<T> fmt::Debug for ObservableCounter<T> {
 }
 
 impl<T> ObservableCounter<T> {
-    /// Records an increment to the counter.
+    /// Records the absolute value of the counter.
     ///
     /// It is only valid to call this within a callback. If called outside of the
     /// registered callback it should have no effect on the instrument, and an
diff --git a/opentelemetry/src/metrics/instruments/up_down_counter.rs b/opentelemetry/src/metrics/instruments/up_down_counter.rs
index 5c92025661..6530191d8e 100644
--- a/opentelemetry/src/metrics/instruments/up_down_counter.rs
+++ b/opentelemetry/src/metrics/instruments/up_down_counter.rs
@@ -88,7 +88,7 @@ impl<T> ObservableUpDownCounter<T> {
         ObservableUpDownCounter(inner)
     }
 
-    /// Records the increment or decrement to the counter.
+    /// Records the absolute value of the counter.
     ///
     /// It is only valid to call this within a callback. If called outside of the
     /// registered callback it should have no effect on the instrument, and an