diff --git a/packages/opentelemetry-propagator-b3/src/B3MultiPropagator.ts b/packages/opentelemetry-propagator-b3/src/B3MultiPropagator.ts
index 17b2a3859d..63189e1578 100644
--- a/packages/opentelemetry-propagator-b3/src/B3MultiPropagator.ts
+++ b/packages/opentelemetry-propagator-b3/src/B3MultiPropagator.ts
@@ -42,7 +42,7 @@ function isValidSampledValue(sampled: TraceFlags | undefined): boolean {
   return sampled === TraceFlags.SAMPLED || sampled === TraceFlags.NONE;
 }
 
-export function parseHeader(header: unknown) {
+function parseHeader(header: unknown) {
   return Array.isArray(header) ? header[0] : header;
 }
 
@@ -93,7 +93,7 @@ function getTraceFlags(
  * Based on: https://github.com/openzipkin/b3-propagation
  */
 export class B3MultiPropagator implements TextMapPropagator {
-  inject(context: Context, carrier: unknown, setter: TextMapSetter) {
+  inject(context: Context, carrier: unknown, setter: TextMapSetter): void {
     const spanContext = trace.getSpanContext(context);
     if (
       !spanContext ||
diff --git a/packages/opentelemetry-propagator-b3/src/B3Propagator.ts b/packages/opentelemetry-propagator-b3/src/B3Propagator.ts
index 760752d84b..cc975ad49e 100644
--- a/packages/opentelemetry-propagator-b3/src/B3Propagator.ts
+++ b/packages/opentelemetry-propagator-b3/src/B3Propagator.ts
@@ -53,7 +53,7 @@ export class B3Propagator implements TextMapPropagator {
     }
   }
 
-  inject(context: Context, carrier: unknown, setter: TextMapSetter) {
+  inject(context: Context, carrier: unknown, setter: TextMapSetter): void {
     if (isTracingSuppressed(context)) {
       return;
     }
diff --git a/packages/opentelemetry-propagator-b3/src/B3SinglePropagator.ts b/packages/opentelemetry-propagator-b3/src/B3SinglePropagator.ts
index 6a26a93265..eb8ac46ac0 100644
--- a/packages/opentelemetry-propagator-b3/src/B3SinglePropagator.ts
+++ b/packages/opentelemetry-propagator-b3/src/B3SinglePropagator.ts
@@ -49,7 +49,7 @@ function convertToTraceFlags(samplingState: string | undefined): TraceFlags {
  * Based on: https://github.com/openzipkin/b3-propagation
  */
 export class B3SinglePropagator implements TextMapPropagator {
-  inject(context: Context, carrier: unknown, setter: TextMapSetter) {
+  inject(context: Context, carrier: unknown, setter: TextMapSetter): void {
     const spanContext = trace.getSpanContext(context);
     if (
       !spanContext ||
diff --git a/packages/opentelemetry-propagator-jaeger/src/JaegerPropagator.ts b/packages/opentelemetry-propagator-jaeger/src/JaegerPropagator.ts
index 252dc39fb5..f3a739f4b9 100644
--- a/packages/opentelemetry-propagator-jaeger/src/JaegerPropagator.ts
+++ b/packages/opentelemetry-propagator-jaeger/src/JaegerPropagator.ts
@@ -55,7 +55,7 @@ export class JaegerPropagator implements TextMapPropagator {
     this._jaegerTraceHeader = customTraceHeader || UBER_TRACE_ID_HEADER;
   }
 
-  inject(context: Context, carrier: unknown, setter: TextMapSetter) {
+  inject(context: Context, carrier: unknown, setter: TextMapSetter): void {
     const spanContext = trace.getSpanContext(context);
     const baggage = propagation.getBaggage(context);
     if (spanContext && isTracingSuppressed(context) === false) {
diff --git a/packages/opentelemetry-resources/src/platform/browser/default-service-name.ts b/packages/opentelemetry-resources/src/platform/browser/default-service-name.ts
index c31f3bedd9..eebfb121e7 100644
--- a/packages/opentelemetry-resources/src/platform/browser/default-service-name.ts
+++ b/packages/opentelemetry-resources/src/platform/browser/default-service-name.ts
@@ -14,6 +14,6 @@
  * limitations under the License.
  */
 
-export function defaultServiceName() {
+export function defaultServiceName(): string {
     return 'unknown_service';
-}
\ No newline at end of file
+}
diff --git a/packages/opentelemetry-resources/src/platform/node/default-service-name.ts b/packages/opentelemetry-resources/src/platform/node/default-service-name.ts
index 0f5b870a63..c1df6d22fb 100644
--- a/packages/opentelemetry-resources/src/platform/node/default-service-name.ts
+++ b/packages/opentelemetry-resources/src/platform/node/default-service-name.ts
@@ -14,6 +14,6 @@
  * limitations under the License.
  */
 
-export function defaultServiceName() {
+export function defaultServiceName(): string {
     return `unknown_service:${process.argv0}`;
-}
\ No newline at end of file
+}
diff --git a/packages/opentelemetry-sdk-metrics-base/src/BaseObserverMetric.ts b/packages/opentelemetry-sdk-metrics-base/src/BaseObserverMetric.ts
index a3098f119c..6f48df49bf 100644
--- a/packages/opentelemetry-sdk-metrics-base/src/BaseObserverMetric.ts
+++ b/packages/opentelemetry-sdk-metrics-base/src/BaseObserverMetric.ts
@@ -14,6 +14,7 @@
  * limitations under the License.
  */
 import * as api from '@opentelemetry/api-metrics';
+import { Observation } from '@opentelemetry/api-metrics';
 import { InstrumentationLibrary } from '@opentelemetry/core';
 import { Resource } from '@opentelemetry/resources';
 import { BoundObserver } from './BoundInstrument';
@@ -64,14 +65,14 @@ export abstract class BaseObserverMetric
     return super.getMetricRecord();
   }
 
-  protected _processResults(observerResult: ObserverResult) {
+  protected _processResults(observerResult: ObserverResult): void {
     observerResult.values.forEach((value, labels) => {
       const instrument = this.bind(labels);
       instrument.update(value);
     });
   }
 
-  observation(value: number) {
+  observation(value: number): Observation {
     return {
       value,
       observer: this as BaseObserverMetric,
diff --git a/packages/opentelemetry-sdk-metrics-base/src/BatchObserverResult.ts b/packages/opentelemetry-sdk-metrics-base/src/BatchObserverResult.ts
index da6d5367e0..4e2c0c8b28 100644
--- a/packages/opentelemetry-sdk-metrics-base/src/BatchObserverResult.ts
+++ b/packages/opentelemetry-sdk-metrics-base/src/BatchObserverResult.ts
@@ -35,7 +35,7 @@ export class BatchObserverResult implements api.BatchObserverResult {
    *     updated
    * @param [callback]
    */
-  onObserveCalled(callback?: () => void) {
+  onObserveCalled(callback?: () => void): void {
     this._callback = callback;
   }
 
diff --git a/packages/opentelemetry-sdk-metrics-base/src/CounterMetric.ts b/packages/opentelemetry-sdk-metrics-base/src/CounterMetric.ts
index 36b4fb70c7..4f4fe3f04d 100644
--- a/packages/opentelemetry-sdk-metrics-base/src/CounterMetric.ts
+++ b/packages/opentelemetry-sdk-metrics-base/src/CounterMetric.ts
@@ -48,7 +48,7 @@ export class CounterMetric extends Metric<BoundCounter> implements api.Counter {
    * @param [labels = {}] key-values pairs that are associated with a specific metric
    *     that you want to record.
    */
-  add(value: number, labels: api.Labels = {}) {
+  add(value: number, labels: api.Labels = {}): void {
     this.bind(labels).add(value);
   }
 }
diff --git a/packages/opentelemetry-sdk-metrics-base/src/MeterProvider.ts b/packages/opentelemetry-sdk-metrics-base/src/MeterProvider.ts
index 1d0cf1f098..226ff63aa6 100644
--- a/packages/opentelemetry-sdk-metrics-base/src/MeterProvider.ts
+++ b/packages/opentelemetry-sdk-metrics-base/src/MeterProvider.ts
@@ -54,6 +54,7 @@ export class MeterProvider implements api.MeterProvider {
       );
     }
 
+    // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
     return this._meters.get(key)!;
   }
 
diff --git a/packages/opentelemetry-sdk-metrics-base/src/Metric.ts b/packages/opentelemetry-sdk-metrics-base/src/Metric.ts
index b753b322ea..fc3cc06664 100644
--- a/packages/opentelemetry-sdk-metrics-base/src/Metric.ts
+++ b/packages/opentelemetry-sdk-metrics-base/src/Metric.ts
@@ -59,6 +59,7 @@ export abstract class Metric<T extends BaseBoundInstrument>
    */
   bind(labels: api.Labels): T {
     const hash = hashLabels(labels);
+    // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
     if (this._instruments.has(hash)) return this._instruments.get(hash)!;
 
     const instrument = this._makeInstrument(labels);
@@ -88,7 +89,7 @@ export abstract class Metric<T extends BaseBoundInstrument>
     return this._kind;
   }
 
-  getAggregationTemporality() {
+  getAggregationTemporality(): api.AggregationTemporality {
     return this._aggregationTemporality;
   }
 
diff --git a/packages/opentelemetry-sdk-metrics-base/src/SumObserverMetric.ts b/packages/opentelemetry-sdk-metrics-base/src/SumObserverMetric.ts
index 7244bc88d4..8f58727ceb 100644
--- a/packages/opentelemetry-sdk-metrics-base/src/SumObserverMetric.ts
+++ b/packages/opentelemetry-sdk-metrics-base/src/SumObserverMetric.ts
@@ -45,7 +45,7 @@ export class SumObserverMetric
     );
   }
 
-  protected override _processResults(observerResult: ObserverResult) {
+  protected override _processResults(observerResult: ObserverResult): void {
     observerResult.values.forEach((value, labels) => {
       const instrument = this.bind(labels);
       // SumObserver is monotonic which means it should only accept values
diff --git a/packages/opentelemetry-sdk-metrics-base/src/UpDownCounterMetric.ts b/packages/opentelemetry-sdk-metrics-base/src/UpDownCounterMetric.ts
index 36650b2336..491a4647dc 100644
--- a/packages/opentelemetry-sdk-metrics-base/src/UpDownCounterMetric.ts
+++ b/packages/opentelemetry-sdk-metrics-base/src/UpDownCounterMetric.ts
@@ -56,7 +56,7 @@ export class UpDownCounterMetric
    * @param [labels = {}] key-values pairs that are associated with a specific
    *     metric that you want to record.
    */
-  add(value: number, labels: api.Labels = {}) {
+  add(value: number, labels: api.Labels = {}): void {
     this.bind(labels).add(value);
   }
 }
diff --git a/packages/opentelemetry-sdk-metrics-base/src/ValueRecorderMetric.ts b/packages/opentelemetry-sdk-metrics-base/src/ValueRecorderMetric.ts
index cda854d8ed..28e9d7e1b2 100644
--- a/packages/opentelemetry-sdk-metrics-base/src/ValueRecorderMetric.ts
+++ b/packages/opentelemetry-sdk-metrics-base/src/ValueRecorderMetric.ts
@@ -51,7 +51,7 @@ export class ValueRecorderMetric
     );
   }
 
-  record(value: number, labels: api.Labels = {}) {
+  record(value: number, labels: api.Labels = {}): void {
     this.bind(labels).record(value);
   }
 }